From 48b8efa7590fcdb09b3f338a7746c9f944257fe8 Mon Sep 17 00:00:00 2001
From: "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
Date: Thu, 4 Mar 2021 02:54:55 +0100
Subject: [PATCH] Fixup OAuth [wip]

---
 .../web/api_spec/operations/o_auth_operation.ex    |  31 +-
 lib/pleroma/web/o_auth/fallback_controller.ex      |   5 +-
 lib/pleroma/web/o_auth/mfa_controller.ex           |   3 +-
 .../web/o_auth/o_auth_browser_controller.ex        | 308 +++++++
 lib/pleroma/web/o_auth/o_auth_controller.ex        | 399 ++-------
 lib/pleroma/web/router.ex                          |  23 +-
 .../web/templates/o_auth/o_auth/show.html.eex      |   2 +-
 .../pleroma/web/o_auth/ldap_authorization_test.exs |  54 +-
 .../web/o_auth/o_auth_browser_controller_test.exs  | 576 +++++++++++++
 test/pleroma/web/o_auth/o_auth_controller_test.exs | 932 +++++----------------
 10 files changed, 1216 insertions(+), 1117 deletions(-)
 create mode 100644 lib/pleroma/web/o_auth/o_auth_browser_controller.ex
 create mode 100644 test/pleroma/web/o_auth/o_auth_browser_controller_test.exs

diff --git a/lib/pleroma/web/api_spec/operations/o_auth_operation.ex b/lib/pleroma/web/api_spec/operations/o_auth_operation.ex
index d507fddd5..cb049e5e8 100644
--- a/lib/pleroma/web/api_spec/operations/o_auth_operation.ex
+++ b/lib/pleroma/web/api_spec/operations/o_auth_operation.ex
@@ -77,8 +77,18 @@ defmodule Pleroma.Web.ApiSpec.OAuthOperation do
           "Set equal to `authorization_code` if `code` is provided in order to gain user-level access. Set equal to `password` if `username` and `password` are provided. Otherwise, set equal to `client_credentials` to obtain app-level access only.",
           required: true
         ),
-        Operation.parameter(:username, :query, :string, "User's username, used with `grant_type=password`"),
-        Operation.parameter(:password, :query, :string, "User's password, used with `grant_type=password`")
+        Operation.parameter(
+          :username,
+          :query,
+          :string,
+          "User's username, used with `grant_type=password`"
+        ),
+        Operation.parameter(
+          :password,
+          :query,
+          :string,
+          "User's password, used with `grant_type=password`"
+        )
       ],
       responses: %{
         200 =>
@@ -161,23 +171,6 @@ defmodule Pleroma.Web.ApiSpec.OAuthOperation do
     }
   end
 
-  def create_authorization_operation do
-    %Operation{
-      tags: ["OAuth"],
-      summary: "Create Authorization",
-      operationId: "OAuthController.create_authorization",
-      parameters: [],
-      responses: %{
-        200 =>
-          Operation.response("Success", "application/json", %Schema{
-            type: :object,
-            properties: %{status: %Schema{type: :string, example: "success"}}
-          }),
-        400 => Operation.response("Error", "application/json", ApiError)
-      }
-    }
-  end
-
   def prepare_request_operation do
     %Operation{
       tags: ["OAuth"],
diff --git a/lib/pleroma/web/o_auth/fallback_controller.ex b/lib/pleroma/web/o_auth/fallback_controller.ex
index df68cbfc1..4bcf12253 100644
--- a/lib/pleroma/web/o_auth/fallback_controller.ex
+++ b/lib/pleroma/web/o_auth/fallback_controller.ex
@@ -4,6 +4,7 @@
 
 defmodule Pleroma.Web.OAuth.FallbackController do
   use Pleroma.Web, :controller
+  alias Pleroma.Web.OAuth.OAuthBrowserController
   alias Pleroma.Web.OAuth.OAuthController
 
   def call(conn, {:register, :generic_error}) do
@@ -13,14 +14,14 @@ defmodule Pleroma.Web.OAuth.FallbackController do
       :error,
       dgettext("errors", "Unknown error, please check the details and try again.")
     )
-    |> OAuthController.registration_details(conn.params)
+    |> OAuthBrowserController.registration_details(conn.params)
   end
 
   def call(conn, {:register, _error}) do
     conn
     |> put_status(:unauthorized)
     |> put_flash(:error, dgettext("errors", "Invalid Username/Password"))
-    |> OAuthController.registration_details(conn.params)
+    |> OAuthBrowserController.registration_details(conn.params)
   end
 
   def call(conn, _error) do
diff --git a/lib/pleroma/web/o_auth/mfa_controller.ex b/lib/pleroma/web/o_auth/mfa_controller.ex
index b38b00213..97b307301 100644
--- a/lib/pleroma/web/o_auth/mfa_controller.ex
+++ b/lib/pleroma/web/o_auth/mfa_controller.ex
@@ -12,6 +12,7 @@ defmodule Pleroma.Web.OAuth.MFAController do
   alias Pleroma.MFA
   alias Pleroma.Web.Auth.TOTPAuthenticator
   alias Pleroma.Web.OAuth.MFAView, as: View
+  alias Pleroma.Web.OAuth.OAuthBrowserController
   alias Pleroma.Web.OAuth.OAuthController
   alias Pleroma.Web.OAuth.Token
 
@@ -40,7 +41,7 @@ defmodule Pleroma.Web.OAuth.MFAController do
     with {:ok, %{user: user, authorization: auth}} <- MFA.Token.validate(mfa_token),
          {:ok, _} <- validates_challenge(user, mfa_params) do
       conn
-      |> OAuthController.after_create_authorization(auth, %{
+      |> OAuthBrowserController.after_create_authorization(auth, %{
         "authorization" => %{
           "redirect_uri" => mfa_params["redirect_uri"],
           "state" => mfa_params["state"]
diff --git a/lib/pleroma/web/o_auth/o_auth_browser_controller.ex b/lib/pleroma/web/o_auth/o_auth_browser_controller.ex
new file mode 100644
index 000000000..3f78f6ef1
--- /dev/null
+++ b/lib/pleroma/web/o_auth/o_auth_browser_controller.ex
@@ -0,0 +1,308 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.OAuth.OAuthBrowserController do
+  use Pleroma.Web, :controller
+
+  alias Pleroma.Helpers.UriHelper
+  alias Pleroma.Maps
+  alias Pleroma.MFA
+  alias Pleroma.Registration
+  alias Pleroma.Repo
+  alias Pleroma.User
+  alias Pleroma.Web.Auth.Authenticator
+  alias Pleroma.Web.OAuth.Authorization
+  alias Pleroma.Web.OAuth.OAuthController
+  alias Pleroma.Web.OAuth.MFAController
+  alias Pleroma.Web.OAuth.OAuthView
+  alias Pleroma.Web.OAuth.Scopes
+  alias Pleroma.Web.Plugs.RateLimiter
+
+  require Logger
+
+  if Pleroma.Config.oauth_consumer_enabled?(), do: plug(Ueberauth)
+
+  plug(:fetch_session)
+  plug(:fetch_flash)
+
+  plug(:skip_plug, [
+    Pleroma.Web.Plugs.OAuthScopesPlug,
+    Pleroma.Web.Plugs.EnsurePublicOrAuthenticatedPlug
+  ])
+
+  plug(RateLimiter, name: :authentication)
+
+  action_fallback(Pleroma.Web.OAuth.FallbackController)
+
+  @oob_token_redirect_uri "urn:ietf:wg:oauth:2.0:oob"
+
+  def authorize_callback(_, _, opts \\ [])
+
+  def authorize_callback(%Plug.Conn{assigns: %{user: %User{} = user}} = conn, params, []) do
+    authorize_callback(conn, params, user: user)
+  end
+
+  def authorize_callback(%Plug.Conn{} = conn, %{"authorization" => _} = params, opts) do
+    with {:ok, auth, user} <- OAuthController.do_create_authorization(conn, params, opts[:user]),
+         {:mfa_required, _, _, false} <- {:mfa_required, user, auth, MFA.require?(user)} do
+      after_create_authorization(conn, auth, params)
+    else
+      error ->
+        handle_create_authorization_error(conn, error, params)
+    end
+  end
+
+  def after_create_authorization(%Plug.Conn{} = conn, %Authorization{} = auth, %{
+        "authorization" => %{"redirect_uri" => @oob_token_redirect_uri}
+      }) do
+    # Enforcing the view to reuse the template when calling from other controllers
+    conn
+    |> put_view(OAuthView)
+    |> render("oob_authorization_created.html", %{auth: auth})
+  end
+
+  def after_create_authorization(%Plug.Conn{} = conn, %Authorization{} = auth, %{
+        "authorization" => %{"redirect_uri" => redirect_uri} = auth_attrs
+      }) do
+    app = Repo.preload(auth, :app).app
+
+    # An extra safety measure before we redirect (also done in `do_create_authorization/2`)
+    if redirect_uri in String.split(app.redirect_uris) do
+      redirect_uri = OAuthController.redirect_uri(conn, redirect_uri)
+      url_params = %{code: auth.token}
+      url_params = Maps.put_if_present(url_params, :state, auth_attrs["state"])
+      url = UriHelper.modify_uri_params(redirect_uri, url_params)
+      redirect(conn, external: url)
+    else
+      conn
+      |> put_flash(:error, dgettext("errors", "Unlisted redirect_uri."))
+      |> redirect(external: OAuthController.redirect_uri(conn, redirect_uri))
+    end
+  end
+
+  defp handle_create_authorization_error(
+         %Plug.Conn{} = conn,
+         {:error, scopes_issue},
+         %{"authorization" => _} = params
+       )
+       when scopes_issue in [:unsupported_scopes, :missing_scopes] do
+    # Per https://github.com/tootsuite/mastodon/blob/
+    #   51e154f5e87968d6bb115e053689767ab33e80cd/app/controllers/api/base_controller.rb#L39
+    conn
+    |> put_flash(:error, dgettext("errors", "This action is outside the authorized scopes"))
+    |> put_status(:unauthorized)
+    |> OAuthController.authorize(params)
+  end
+
+  defp handle_create_authorization_error(
+         %Plug.Conn{} = conn,
+         {:account_status, :confirmation_pending},
+         %{"authorization" => _} = params
+       ) do
+    conn
+    |> put_flash(:error, dgettext("errors", "Your login is missing a confirmed e-mail address"))
+    |> put_status(:forbidden)
+    |> OAuthController.authorize(params)
+  end
+
+  defp handle_create_authorization_error(
+         %Plug.Conn{} = conn,
+         {:mfa_required, user, auth, _},
+         params
+       ) do
+    {:ok, token} = MFA.Token.create(user, auth)
+
+    data = %{
+      "mfa_token" => token.token,
+      "redirect_uri" => params["authorization"]["redirect_uri"],
+      "state" => params["authorization"]["state"]
+    }
+
+    MFAController.show(conn, data)
+  end
+
+  defp handle_create_authorization_error(
+         %Plug.Conn{} = conn,
+         {:account_status, :password_reset_pending},
+         %{"authorization" => _} = params
+       ) do
+    conn
+    |> put_flash(:error, dgettext("errors", "Password reset is required"))
+    |> put_status(:forbidden)
+    |> OAuthController.authorize(params)
+  end
+
+  defp handle_create_authorization_error(
+         %Plug.Conn{} = conn,
+         {:account_status, :deactivated},
+         %{"authorization" => _} = params
+       ) do
+    conn
+    |> put_flash(:error, dgettext("errors", "Your account is currently disabled"))
+    |> put_status(:forbidden)
+    |> OAuthController.authorize(params)
+  end
+
+  defp handle_create_authorization_error(%Plug.Conn{} = conn, error, %{"authorization" => _}) do
+    Authenticator.handle_error(conn, error)
+  end
+
+  @doc "Prepares OAuth request to provider for Ueberauth"
+  def prepare_request(%Plug.Conn{} = conn, %{
+        "provider" => provider,
+        "authorization" => auth_attrs
+      }) do
+    scope =
+      auth_attrs
+      |> Scopes.fetch_scopes([])
+      |> Scopes.to_string()
+
+    state =
+      auth_attrs
+      |> Map.delete("scopes")
+      |> Map.put("scope", scope)
+      |> Jason.encode!()
+
+    params =
+      auth_attrs
+      |> Map.drop(~w(scope scopes client_id redirect_uri))
+      |> Map.put("state", state)
+
+    # Handing the request to Ueberauth
+    redirect(conn, to: o_auth_browser_path(conn, :provider_request, provider, params))
+  end
+
+  def provider_request(%Plug.Conn{} = conn, params) do
+    message =
+      if params["provider"] do
+        dgettext("errors", "Unsupported OAuth provider: %{provider}.",
+          provider: params["provider"]
+        )
+      else
+        dgettext("errors", "Bad OAuth request.")
+      end
+
+    conn
+    |> put_flash(:error, message)
+    |> redirect(to: "/")
+  end
+
+  def provider_callback(%Plug.Conn{assigns: %{ueberauth_failure: failure}} = conn, params) do
+    params = callback_params(params)
+    messages = for e <- Map.get(failure, :errors, []), do: e.message
+    message = Enum.join(messages, "; ")
+
+    conn
+    |> put_flash(
+      :error,
+      dgettext("errors", "Failed to authenticate: %{message}.", message: message)
+    )
+    |> redirect(external: OAuthController.redirect_uri(conn, params["redirect_uri"]))
+  end
+
+  def provider_callback(%Plug.Conn{} = conn, params) do
+    params = callback_params(params)
+
+    with {:ok, registration} <- Authenticator.get_registration(conn) do
+      auth_attrs = Map.take(params, ~w(client_id redirect_uri scope scopes state))
+
+      case Repo.get_assoc(registration, :user) do
+        {:ok, user} ->
+          authorize_callback(conn, %{"authorization" => auth_attrs}, user: user)
+
+        _ ->
+          registration_params =
+            Map.merge(auth_attrs, %{
+              "nickname" => Registration.nickname(registration),
+              "email" => Registration.email(registration)
+            })
+
+          conn
+          |> put_session_registration_id(registration.id)
+          |> registration_details(%{authorization: registration_params})
+      end
+    else
+      error ->
+        Logger.debug(inspect(["OAUTH_ERROR", error, conn.assigns]))
+
+        conn
+        |> put_flash(:error, dgettext("errors", "Failed to set up user account."))
+        |> redirect(external: OAuthController.redirect_uri(conn, params["redirect_uri"]))
+    end
+  end
+
+  defp callback_params(%{"state" => state} = params) do
+    Map.merge(params, Jason.decode!(state))
+  end
+
+  def registration_details(%Plug.Conn{} = conn, %{"authorization" => auth_attrs}) do
+    render(conn, "register.html", %{
+      client_id: auth_attrs["client_id"],
+      redirect_uri: auth_attrs["redirect_uri"],
+      state: auth_attrs["state"],
+      scopes: Scopes.fetch_scopes(auth_attrs, []),
+      nickname: auth_attrs["nickname"],
+      email: auth_attrs["email"]
+    })
+  end
+
+  def register(%Plug.Conn{} = conn, %{"authorization" => _, "op" => "connect"} = params) do
+    with registration_id when not is_nil(registration_id) <- get_session_registration_id(conn),
+         %Registration{} = registration <- Repo.get(Registration, registration_id),
+         {_, {:ok, auth, _user}} <-
+           {:create_authorization, OAuthController.do_create_authorization(conn, params)},
+         %User{} = user <- Repo.preload(auth, :user).user,
+         {:ok, _updated_registration} <- Registration.bind_to_user(registration, user) do
+      conn
+      |> put_session_registration_id(nil)
+      |> after_create_authorization(auth, params)
+    else
+      {:create_authorization, error} ->
+        {:register, handle_create_authorization_error(conn, error, params)}
+
+      _ ->
+        {:register, :generic_error}
+    end
+  end
+
+  def register(%Plug.Conn{} = conn, %{"authorization" => _, "op" => "register"} = params) do
+    with registration_id when not is_nil(registration_id) <- get_session_registration_id(conn),
+         %Registration{} = registration <- Repo.get(Registration, registration_id),
+         {:ok, user} <- Authenticator.create_from_registration(conn, registration) do
+      conn
+      |> put_session_registration_id(nil)
+      |> authorize_callback(
+        params,
+        user: user
+      )
+    else
+      {:error, changeset} ->
+        message =
+          Enum.map(changeset.errors, fn {field, {error, _}} ->
+            "#{field} #{error}"
+          end)
+          |> Enum.join("; ")
+
+        message =
+          String.replace(
+            message,
+            "ap_id has already been taken",
+            "nickname has already been taken"
+          )
+
+        conn
+        |> put_status(:forbidden)
+        |> put_flash(:error, "Error: #{message}.")
+        |> registration_details(params)
+
+      _ ->
+        {:register, :generic_error}
+    end
+  end
+
+  defp get_session_registration_id(%Plug.Conn{} = conn), do: get_session(conn, :registration_id)
+
+  defp put_session_registration_id(%Plug.Conn{} = conn, registration_id),
+    do: put_session(conn, :registration_id, registration_id)
+end
diff --git a/lib/pleroma/web/o_auth/o_auth_controller.ex b/lib/pleroma/web/o_auth/o_auth_controller.ex
index 741f57195..8087c6754 100644
--- a/lib/pleroma/web/o_auth/o_auth_controller.ex
+++ b/lib/pleroma/web/o_auth/o_auth_controller.ex
@@ -7,16 +7,14 @@ defmodule Pleroma.Web.OAuth.OAuthController do
 
   alias Pleroma.Helpers.AuthHelper
   alias Pleroma.Helpers.UriHelper
-  alias Pleroma.Maps
   alias Pleroma.MFA
-  alias Pleroma.Registration
+  alias Pleroma.Maps
   alias Pleroma.Repo
   alias Pleroma.User
   alias Pleroma.Web.Auth.Authenticator
   alias Pleroma.Web.ControllerHelper
   alias Pleroma.Web.OAuth.App
   alias Pleroma.Web.OAuth.Authorization
-  alias Pleroma.Web.OAuth.MFAController
   alias Pleroma.Web.OAuth.MFAView
   alias Pleroma.Web.OAuth.OAuthView
   alias Pleroma.Web.OAuth.Scopes
@@ -25,14 +23,9 @@ defmodule Pleroma.Web.OAuth.OAuthController do
   alias Pleroma.Web.OAuth.Token.Strategy.Revoke, as: RevokeToken
   alias Pleroma.Web.Plugs.RateLimiter
 
-  require Logger
-
   if Pleroma.Config.oauth_consumer_enabled?(), do: plug(Ueberauth)
 
-  plug(
-    Pleroma.Web.ApiSpec.CastAndValidate
-    when action not in [:prepare_request, :callback, :request, :register]
-  )
+  plug(Pleroma.Web.ApiSpec.CastAndValidate)
 
   plug(:fetch_session)
   plug(:fetch_flash)
@@ -42,7 +35,7 @@ defmodule Pleroma.Web.OAuth.OAuthController do
     Pleroma.Web.Plugs.EnsurePublicOrAuthenticatedPlug
   ])
 
-  plug(RateLimiter, [name: :authentication] when action == :create_authorization)
+  plug(RateLimiter, name: :authentication)
 
   action_fallback(Pleroma.Web.OAuth.FallbackController)
 
@@ -148,117 +141,6 @@ defmodule Pleroma.Web.OAuth.OAuthController do
     end
   end
 
-  def create_authorization(_, _, opts \\ [])
-
-  def create_authorization(%Plug.Conn{assigns: %{user: %User{} = user}} = conn, params, []) do
-    create_authorization(conn, params, user: user)
-  end
-
-  def create_authorization(%Plug.Conn{} = conn, %{authorization: _} = params, opts) do
-    with {:ok, auth, user} <- do_create_authorization(conn, params, opts[:user]),
-         {:mfa_required, _, _, false} <- {:mfa_required, user, auth, MFA.require?(user)} do
-      after_create_authorization(conn, auth, params)
-    else
-      error ->
-        handle_create_authorization_error(conn, error, params)
-    end
-  end
-
-  def after_create_authorization(%Plug.Conn{} = conn, %Authorization{} = auth, %{
-        "authorization" => %{"redirect_uri" => @oob_token_redirect_uri}
-      }) do
-    # Enforcing the view to reuse the template when calling from other controllers
-    conn
-    |> put_view(OAuthView)
-    |> render("oob_authorization_created.html", %{auth: auth})
-  end
-
-  def after_create_authorization(%Plug.Conn{} = conn, %Authorization{} = auth, %{
-        "authorization" => %{"redirect_uri" => redirect_uri} = auth_attrs
-      }) do
-    app = Repo.preload(auth, :app).app
-
-    # An extra safety measure before we redirect (also done in `do_create_authorization/2`)
-    if redirect_uri in String.split(app.redirect_uris) do
-      redirect_uri = redirect_uri(conn, redirect_uri)
-      url_params = %{code: auth.token}
-      url_params = Maps.put_if_present(url_params, :state, auth_attrs["state"])
-      url = UriHelper.modify_uri_params(redirect_uri, url_params)
-      redirect(conn, external: url)
-    else
-      conn
-      |> put_flash(:error, dgettext("errors", "Unlisted redirect_uri."))
-      |> redirect(external: redirect_uri(conn, redirect_uri))
-    end
-  end
-
-  defp handle_create_authorization_error(
-         %Plug.Conn{} = conn,
-         {:error, scopes_issue},
-         %{"authorization" => _} = params
-       )
-       when scopes_issue in [:unsupported_scopes, :missing_scopes] do
-    # Per https://github.com/tootsuite/mastodon/blob/
-    #   51e154f5e87968d6bb115e053689767ab33e80cd/app/controllers/api/base_controller.rb#L39
-    conn
-    |> put_flash(:error, dgettext("errors", "This action is outside the authorized scopes"))
-    |> put_status(:unauthorized)
-    |> authorize(params)
-  end
-
-  defp handle_create_authorization_error(
-         %Plug.Conn{} = conn,
-         {:account_status, :confirmation_pending},
-         %{"authorization" => _} = params
-       ) do
-    conn
-    |> put_flash(:error, dgettext("errors", "Your login is missing a confirmed e-mail address"))
-    |> put_status(:forbidden)
-    |> authorize(params)
-  end
-
-  defp handle_create_authorization_error(
-         %Plug.Conn{} = conn,
-         {:mfa_required, user, auth, _},
-         params
-       ) do
-    {:ok, token} = MFA.Token.create(user, auth)
-
-    data = %{
-      "mfa_token" => token.token,
-      "redirect_uri" => params["authorization"]["redirect_uri"],
-      "state" => params["authorization"]["state"]
-    }
-
-    MFAController.show(conn, data)
-  end
-
-  defp handle_create_authorization_error(
-         %Plug.Conn{} = conn,
-         {:account_status, :password_reset_pending},
-         %{"authorization" => _} = params
-       ) do
-    conn
-    |> put_flash(:error, dgettext("errors", "Password reset is required"))
-    |> put_status(:forbidden)
-    |> authorize(params)
-  end
-
-  defp handle_create_authorization_error(
-         %Plug.Conn{} = conn,
-         {:account_status, :deactivated},
-         %{"authorization" => _} = params
-       ) do
-    conn
-    |> put_flash(:error, dgettext("errors", "Your account is currently disabled"))
-    |> put_status(:forbidden)
-    |> authorize(params)
-  end
-
-  defp handle_create_authorization_error(%Plug.Conn{} = conn, error, %{"authorization" => _}) do
-    Authenticator.handle_error(conn, error)
-  end
-
   @doc "Renew access_token with refresh_token"
   def token_exchange(
         %Plug.Conn{} = conn,
@@ -325,7 +207,49 @@ defmodule Pleroma.Web.OAuth.OAuthController do
   end
 
   # Bad request
-  def token_exchange(%Plug.Conn{} = conn, params), do: bad_request(conn, params)
+  def token_exchange(%Plug.Conn{} = _conn, _params), do: {:error, :bad_request}
+
+  # Note: intended to be a private function but opened for AccountController that logs in on signup
+  @doc "If checks pass, creates authorization and token for given user, app and requested scopes."
+  def login(%User{} = user, %App{} = app, requested_scopes) when is_list(requested_scopes) do
+    with {:ok, auth} <- do_create_authorization(user, app, requested_scopes),
+         {:mfa_required, _, _, false} <- {:mfa_required, user, auth, MFA.require?(user)},
+         {:ok, token} <- Token.exchange_token(app, auth) do
+      {:ok, token}
+    end
+  end
+
+  def do_create_authorization(conn, auth_attrs, user \\ nil)
+
+  def do_create_authorization(
+        %Plug.Conn{} = conn,
+        %{
+          "authorization" =>
+            %{
+              "client_id" => client_id,
+              "redirect_uri" => redirect_uri
+            } = auth_attrs
+        },
+        user
+      ) do
+    with {_, {:ok, %User{} = user}} <-
+           {:get_user, (user && {:ok, user}) || Authenticator.get_user(conn)},
+         %App{} = app <- Repo.get_by(App, client_id: client_id),
+         true <- redirect_uri in String.split(app.redirect_uris),
+         requested_scopes <- Scopes.fetch_scopes(auth_attrs, app.scopes),
+         {:ok, auth} <- do_create_authorization(user, app, requested_scopes) do
+      {:ok, auth, user}
+    end
+  end
+
+  def do_create_authorization(%User{} = user, %App{} = app, requested_scopes)
+      when is_list(requested_scopes) do
+    with {:account_status, :active} <- {:account_status, User.account_status(user)},
+         {:ok, scopes} <- validate_scopes(app, requested_scopes),
+         {:ok, auth} <- Authorization.create_authorization(app, user, scopes) do
+      {:ok, auth}
+    end
+  end
 
   def after_token_exchange(%Plug.Conn{} = conn, %{token: token} = view_params) do
     conn
@@ -386,6 +310,16 @@ defmodule Pleroma.Web.OAuth.OAuthController do
     render_invalid_credentials_error(conn)
   end
 
+  defp render_invalid_credentials_error(conn) do
+    render_error(conn, :bad_request, "Invalid credentials")
+  end
+
+  defp build_and_response_mfa_token(user, auth) do
+    with {:ok, token} <- MFA.Token.create(user, auth) do
+      MFAView.render("mfa_response.json", %{token: token, user: user})
+    end
+  end
+
   def token_revoke(%Plug.Conn{} = conn, %{token: token}) do
     with {:ok, %Token{} = oauth_token} <- Token.get_by_token(token),
          {:ok, oauth_token} <- RevokeToken.revoke(oauth_token) do
@@ -405,223 +339,12 @@ defmodule Pleroma.Web.OAuth.OAuthController do
     end
   end
 
-  def token_revoke(%Plug.Conn{} = conn, params), do: bad_request(conn, params)
-
-  # Response for bad request
-  defp bad_request(%Plug.Conn{} = conn, _) do
-    render_error(conn, :internal_server_error, "Bad request")
-  end
-
-  @doc "Prepares OAuth request to provider for Ueberauth"
-  def prepare_request(%Plug.Conn{} = conn, %{
-        "provider" => provider,
-        "authorization" => auth_attrs
-      }) do
-    scope =
-      auth_attrs
-      |> Scopes.fetch_scopes([])
-      |> Scopes.to_string()
-
-    state =
-      auth_attrs
-      |> Map.delete("scopes")
-      |> Map.put("scope", scope)
-      |> Jason.encode!()
-
-    params =
-      auth_attrs
-      |> Map.drop(~w(scope scopes client_id redirect_uri))
-      |> Map.put("state", state)
-
-    # Handing the request to Ueberauth
-    redirect(conn, to: o_auth_path(conn, :request, provider, params))
-  end
-
-  def request(%Plug.Conn{} = conn, params) do
-    message =
-      if params["provider"] do
-        dgettext("errors", "Unsupported OAuth provider: %{provider}.",
-          provider: params["provider"]
-        )
-      else
-        dgettext("errors", "Bad OAuth request.")
-      end
-
-    conn
-    |> put_flash(:error, message)
-    |> redirect(to: "/")
-  end
-
-  def callback(%Plug.Conn{assigns: %{ueberauth_failure: failure}} = conn, params) do
-    params = callback_params(params)
-    messages = for e <- Map.get(failure, :errors, []), do: e.message
-    message = Enum.join(messages, "; ")
-
-    conn
-    |> put_flash(
-      :error,
-      dgettext("errors", "Failed to authenticate: %{message}.", message: message)
-    )
-    |> redirect(external: redirect_uri(conn, params["redirect_uri"]))
-  end
-
-  def callback(%Plug.Conn{} = conn, params) do
-    params = callback_params(params)
-
-    with {:ok, registration} <- Authenticator.get_registration(conn) do
-      auth_attrs = Map.take(params, ~w(client_id redirect_uri scope scopes state))
-
-      case Repo.get_assoc(registration, :user) do
-        {:ok, user} ->
-          create_authorization(conn, %{"authorization" => auth_attrs}, user: user)
-
-        _ ->
-          registration_params =
-            Map.merge(auth_attrs, %{
-              "nickname" => Registration.nickname(registration),
-              "email" => Registration.email(registration)
-            })
-
-          conn
-          |> put_session_registration_id(registration.id)
-          |> registration_details(%{authorization: registration_params})
-      end
-    else
-      error ->
-        Logger.debug(inspect(["OAUTH_ERROR", error, conn.assigns]))
-
-        conn
-        |> put_flash(:error, dgettext("errors", "Failed to set up user account."))
-        |> redirect(external: redirect_uri(conn, params["redirect_uri"]))
-    end
-  end
-
-  defp callback_params(%{"state" => state} = params) do
-    Map.merge(params, Jason.decode!(state))
-  end
-
-  def registration_details(%Plug.Conn{} = conn, %{authorization: auth_attrs}) do
-    render(conn, "register.html", %{
-      client_id: auth_attrs["client_id"],
-      redirect_uri: auth_attrs["redirect_uri"],
-      state: auth_attrs["state"],
-      scopes: Scopes.fetch_scopes(auth_attrs, []),
-      nickname: auth_attrs["nickname"],
-      email: auth_attrs["email"]
-    })
-  end
-
-  def register(%Plug.Conn{} = conn, %{"authorization" => _, "op" => "connect"} = params) do
-    with registration_id when not is_nil(registration_id) <- get_session_registration_id(conn),
-         %Registration{} = registration <- Repo.get(Registration, registration_id),
-         {_, {:ok, auth, _user}} <-
-           {:create_authorization, do_create_authorization(conn, params)},
-         %User{} = user <- Repo.preload(auth, :user).user,
-         {:ok, _updated_registration} <- Registration.bind_to_user(registration, user) do
-      conn
-      |> put_session_registration_id(nil)
-      |> after_create_authorization(auth, params)
-    else
-      {:create_authorization, error} ->
-        {:register, handle_create_authorization_error(conn, error, params)}
-
-      _ ->
-        {:register, :generic_error}
-    end
-  end
-
-  def register(%Plug.Conn{} = conn, %{"authorization" => _, "op" => "register"} = params) do
-    with registration_id when not is_nil(registration_id) <- get_session_registration_id(conn),
-         %Registration{} = registration <- Repo.get(Registration, registration_id),
-         {:ok, user} <- Authenticator.create_from_registration(conn, registration) do
-      conn
-      |> put_session_registration_id(nil)
-      |> create_authorization(
-        params,
-        user: user
-      )
-    else
-      {:error, changeset} ->
-        message =
-          Enum.map(changeset.errors, fn {field, {error, _}} ->
-            "#{field} #{error}"
-          end)
-          |> Enum.join("; ")
-
-        message =
-          String.replace(
-            message,
-            "ap_id has already been taken",
-            "nickname has already been taken"
-          )
-
-        conn
-        |> put_status(:forbidden)
-        |> put_flash(:error, "Error: #{message}.")
-        |> registration_details(params)
-
-      _ ->
-        {:register, :generic_error}
-    end
-  end
-
-  defp do_create_authorization(conn, auth_attrs, user \\ nil)
-
-  defp do_create_authorization(
-         %Plug.Conn{} = conn,
-         %{
-           "authorization" =>
-             %{
-               "client_id" => client_id,
-               "redirect_uri" => redirect_uri
-             } = auth_attrs
-         },
-         user
-       ) do
-    with {_, {:ok, %User{} = user}} <-
-           {:get_user, (user && {:ok, user}) || Authenticator.get_user(conn)},
-         %App{} = app <- Repo.get_by(App, client_id: client_id),
-         true <- redirect_uri in String.split(app.redirect_uris),
-         requested_scopes <- Scopes.fetch_scopes(auth_attrs, app.scopes),
-         {:ok, auth} <- do_create_authorization(user, app, requested_scopes) do
-      {:ok, auth, user}
-    end
-  end
-
-  defp do_create_authorization(%User{} = user, %App{} = app, requested_scopes)
-       when is_list(requested_scopes) do
-    with {:account_status, :active} <- {:account_status, User.account_status(user)},
-         {:ok, scopes} <- validate_scopes(app, requested_scopes),
-         {:ok, auth} <- Authorization.create_authorization(app, user, scopes) do
-      {:ok, auth}
-    end
-  end
-
-  # Note: intended to be a private function but opened for AccountController that logs in on signup
-  @doc "If checks pass, creates authorization and token for given user, app and requested scopes."
-  def login(%User{} = user, %App{} = app, requested_scopes) when is_list(requested_scopes) do
-    with {:ok, auth} <- do_create_authorization(user, app, requested_scopes),
-         {:mfa_required, _, _, false} <- {:mfa_required, user, auth, MFA.require?(user)},
-         {:ok, token} <- Token.exchange_token(app, auth) do
-      {:ok, token}
-    end
-  end
+  def token_revoke(%Plug.Conn{} = _conn, _params), do: {:error, :bad_request}
 
   # Special case: Local MastodonFE
-  defp redirect_uri(%Plug.Conn{} = conn, "."), do: auth_url(conn, :login)
+  def redirect_uri(%Plug.Conn{} = conn, "."), do: auth_url(conn, :login)
 
-  defp redirect_uri(%Plug.Conn{}, redirect_uri), do: redirect_uri
-
-  defp get_session_registration_id(%Plug.Conn{} = conn), do: get_session(conn, :registration_id)
-
-  defp put_session_registration_id(%Plug.Conn{} = conn, registration_id),
-    do: put_session(conn, :registration_id, registration_id)
-
-  defp build_and_response_mfa_token(user, auth) do
-    with {:ok, token} <- MFA.Token.create(user, auth) do
-      MFAView.render("mfa_response.json", %{token: token, user: user})
-    end
-  end
+  def redirect_uri(%Plug.Conn{}, redirect_uri), do: redirect_uri
 
   @spec validate_scopes(App.t(), map() | list()) ::
           {:ok, list()} | {:error, :missing_scopes | :unsupported_scopes}
@@ -639,8 +362,4 @@ defmodule Pleroma.Web.OAuth.OAuthController do
     |> String.split()
     |> Enum.at(0)
   end
-
-  defp render_invalid_credentials_error(conn) do
-    render_error(conn, :bad_request, "Invalid credentials")
-  end
 end
diff --git a/lib/pleroma/web/router.ex b/lib/pleroma/web/router.ex
index 34df3f365..376c33ee1 100644
--- a/lib/pleroma/web/router.ex
+++ b/lib/pleroma/web/router.ex
@@ -40,6 +40,10 @@ defmodule Pleroma.Web.Router do
     plug(Pleroma.Web.Plugs.OAuthPlug)
     plug(Pleroma.Web.Plugs.UserEnabledPlug)
     plug(Pleroma.Web.Plugs.EnsureUserTokenAssignsPlug)
+  end
+
+  pipeline :oauth_api do
+    plug(:oauth)
     plug(OpenApiSpex.Plug.PutApiSpec, module: Pleroma.Web.ApiSpec)
   end
 
@@ -337,16 +341,21 @@ defmodule Pleroma.Web.Router do
   scope "/oauth", Pleroma.Web.OAuth do
     # Note: use /api/v1/accounts/verify_credentials for userinfo of signed-in user
 
-    get("/registration_details", OAuthController, :registration_details)
+    get("/registration_details", OAuthBrowserController, :registration_details)
 
     post("/mfa/verify", MFAController, :verify, as: :mfa_verify)
     get("/mfa", MFAController, :show)
 
     scope [] do
-      pipe_through(:oauth)
+      pipe_through(:oauth_api)
 
       get("/authorize", OAuthController, :authorize)
-      post("/authorize", OAuthController, :create_authorization)
+    end
+
+    scope [] do
+      pipe_through(:oauth)
+
+      post("/authorize_callback", OAuthBrowserController, :authorize_callback)
     end
 
     scope [] do
@@ -360,10 +369,10 @@ defmodule Pleroma.Web.Router do
     scope [] do
       pipe_through(:browser)
 
-      get("/prepare_request", OAuthController, :prepare_request)
-      get("/:provider", OAuthController, :request)
-      get("/:provider/callback", OAuthController, :callback)
-      post("/register", OAuthController, :register)
+      get("/prepare_request", OAuthBrowserController, :prepare_request)
+      get("/:provider", OAuthBrowserController, :provider_request)
+      get("/:provider/callback", OAuthBrowserController, :provider_callback)
+      post("/register", OAuthBrowserController, :register)
     end
   end
 
diff --git a/lib/pleroma/web/templates/o_auth/o_auth/show.html.eex b/lib/pleroma/web/templates/o_auth/o_auth/show.html.eex
index 1a85818ec..5a063a923 100644
--- a/lib/pleroma/web/templates/o_auth/o_auth/show.html.eex
+++ b/lib/pleroma/web/templates/o_auth/o_auth/show.html.eex
@@ -5,7 +5,7 @@
 <p class="alert alert-danger" role="alert"><%= get_flash(@conn, :error) %></p>
 <% end %>
 
-<%= form_for @conn, o_auth_path(@conn, :authorize), [as: "authorization"], fn f -> %>
+<%= form_for @conn, o_auth_path(@conn, :authorize_callback), [as: "authorization"], fn f -> %>
 
 <%= if @user do %>
   <div class="account-header">
diff --git a/test/pleroma/web/o_auth/ldap_authorization_test.exs b/test/pleroma/web/o_auth/ldap_authorization_test.exs
index a839ed4a7..ae5ffcf41 100644
--- a/test/pleroma/web/o_auth/ldap_authorization_test.exs
+++ b/test/pleroma/web/o_auth/ldap_authorization_test.exs
@@ -37,13 +37,17 @@ defmodule Pleroma.Web.OAuth.LDAPAuthorizationTest do
     ] do
       conn =
         build_conn()
-        |> post("/oauth/token?#{URI.encode_query(%{
-          "grant_type" => "password",
-          "username" => user.nickname,
-          "password" => password,
-          "client_id" => app.client_id,
-          "client_secret" => app.client_secret
-        })}")
+        |> post(
+          "/oauth/token?#{
+            URI.encode_query(%{
+              "grant_type" => "password",
+              "username" => user.nickname,
+              "password" => password,
+              "client_id" => app.client_id,
+              "client_secret" => app.client_secret
+            })
+          }"
+        )
 
       assert %{"access_token" => token} = json_response_and_validate_schema(conn, 200)
 
@@ -81,13 +85,17 @@ defmodule Pleroma.Web.OAuth.LDAPAuthorizationTest do
     ] do
       conn =
         build_conn()
-        |> post("/oauth/token?#{URI.encode_query(%{
-          "grant_type" => "password",
-          "username" => user.nickname,
-          "password" => password,
-          "client_id" => app.client_id,
-          "client_secret" => app.client_secret
-        })}")
+        |> post(
+          "/oauth/token?#{
+            URI.encode_query(%{
+              "grant_type" => "password",
+              "username" => user.nickname,
+              "password" => password,
+              "client_id" => app.client_id,
+              "client_secret" => app.client_secret
+            })
+          }"
+        )
 
       assert %{"access_token" => token} = json_response_and_validate_schema(conn, 200)
 
@@ -120,13 +128,17 @@ defmodule Pleroma.Web.OAuth.LDAPAuthorizationTest do
     ] do
       conn =
         build_conn()
-        |> post("/oauth/token?#{URI.encode_query(%{
-          "grant_type" => "password",
-          "username" => user.nickname,
-          "password" => password,
-          "client_id" => app.client_id,
-          "client_secret" => app.client_secret
-        })}")
+        |> post(
+          "/oauth/token?#{
+            URI.encode_query(%{
+              "grant_type" => "password",
+              "username" => user.nickname,
+              "password" => password,
+              "client_id" => app.client_id,
+              "client_secret" => app.client_secret
+            })
+          }"
+        )
 
       assert %{"error" => "Invalid credentials"} = json_response_and_validate_schema(conn, 400)
       assert_received :close_connection
diff --git a/test/pleroma/web/o_auth/o_auth_browser_controller_test.exs b/test/pleroma/web/o_auth/o_auth_browser_controller_test.exs
new file mode 100644
index 000000000..278af5d95
--- /dev/null
+++ b/test/pleroma/web/o_auth/o_auth_browser_controller_test.exs
@@ -0,0 +1,576 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.OAuth.OAuthBrowserControllerTest do
+  use Pleroma.Web.ConnCase
+
+  import Pleroma.Factory
+
+  alias Pleroma.Helpers.AuthHelper
+  alias Pleroma.MFA
+  alias Pleroma.MFA.TOTP
+  alias Pleroma.Repo
+  alias Pleroma.Web.OAuth.Authorization
+  alias Pleroma.Web.OAuth.OAuthController
+
+  @session_opts [
+    store: :cookie,
+    key: "_test",
+    signing_salt: "cooldude"
+  ]
+  setup do
+    clear_config([:instance, :account_activation_required])
+    clear_config([:instance, :account_approval_required])
+  end
+
+  describe "in OAuth consumer mode, " do
+    setup do
+      [
+        app: insert(:oauth_app),
+        conn:
+          build_conn()
+          |> Plug.Session.call(Plug.Session.init(@session_opts))
+          |> fetch_session()
+      ]
+    end
+
+    setup do: clear_config([:auth, :oauth_consumer_strategies], ~w(twitter facebook))
+
+    test "GET /oauth/prepare_request encodes parameters as `state` and redirects", %{
+      app: app,
+      conn: conn
+    } do
+      conn =
+        get(
+          conn,
+          "/oauth/prepare_request",
+          %{
+            "provider" => "twitter",
+            "authorization" => %{
+              "scope" => "read follow",
+              "client_id" => app.client_id,
+              "redirect_uri" => OAuthController.default_redirect_uri(app),
+              "state" => "a_state"
+            }
+          }
+        )
+
+      assert html_response(conn, 302)
+
+      redirect_query = URI.parse(redirected_to(conn)).query
+      assert %{"state" => state_param} = URI.decode_query(redirect_query)
+      assert {:ok, state_components} = Jason.decode(state_param)
+
+      expected_client_id = app.client_id
+      expected_redirect_uri = app.redirect_uris
+
+      assert %{
+               "scope" => "read follow",
+               "client_id" => ^expected_client_id,
+               "redirect_uri" => ^expected_redirect_uri,
+               "state" => "a_state"
+             } = state_components
+    end
+
+    test "with user-bound registration, GET /oauth/<provider>/callback redirects to `redirect_uri` with `code`",
+         %{app: app, conn: conn} do
+      registration = insert(:registration)
+      redirect_uri = OAuthController.default_redirect_uri(app)
+
+      state_params = %{
+        "scope" => Enum.join(app.scopes, " "),
+        "client_id" => app.client_id,
+        "redirect_uri" => redirect_uri,
+        "state" => ""
+      }
+
+      conn =
+        conn
+        |> assign(:ueberauth_auth, %{provider: registration.provider, uid: registration.uid})
+        |> get(
+          "/oauth/twitter/callback",
+          %{
+            "oauth_token" => "G-5a3AAAAAAAwMH9AAABaektfSM",
+            "oauth_verifier" => "QZl8vUqNvXMTKpdmUnGejJxuHG75WWWs",
+            "provider" => "twitter",
+            "state" => Jason.encode!(state_params)
+          }
+        )
+
+      assert html_response(conn, 302)
+      assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
+    end
+
+    test "with user-unbound registration, GET /oauth/<provider>/callback renders registration_details page",
+         %{app: app, conn: conn} do
+      user = insert(:user)
+
+      state_params = %{
+        "scope" => "read write",
+        "client_id" => app.client_id,
+        "redirect_uri" => OAuthController.default_redirect_uri(app),
+        "state" => "a_state"
+      }
+
+      conn =
+        conn
+        |> assign(:ueberauth_auth, %{
+          provider: "twitter",
+          uid: "171799000",
+          info: %{nickname: user.nickname, email: user.email, name: user.name, description: nil}
+        })
+        |> get(
+          "/oauth/twitter/callback",
+          %{
+            "oauth_token" => "G-5a3AAAAAAAwMH9AAABaektfSM",
+            "oauth_verifier" => "QZl8vUqNvXMTKpdmUnGejJxuHG75WWWs",
+            "provider" => "twitter",
+            "state" => Jason.encode!(state_params)
+          }
+        )
+
+      assert response = html_response(conn, 200)
+      assert response =~ ~r/name="op" type="submit" value="register"/
+      assert response =~ ~r/name="op" type="submit" value="connect"/
+      assert response =~ user.email
+      assert response =~ user.nickname
+    end
+
+    test "on authentication error, GET /oauth/<provider>/callback redirects to `redirect_uri`", %{
+      app: app,
+      conn: conn
+    } do
+      state_params = %{
+        "scope" => Enum.join(app.scopes, " "),
+        "client_id" => app.client_id,
+        "redirect_uri" => OAuthController.default_redirect_uri(app),
+        "state" => ""
+      }
+
+      conn =
+        conn
+        |> assign(:ueberauth_failure, %{errors: [%{message: "(error description)"}]})
+        |> get(
+          "/oauth/twitter/callback",
+          %{
+            "oauth_token" => "G-5a3AAAAAAAwMH9AAABaektfSM",
+            "oauth_verifier" => "QZl8vUqNvXMTKpdmUnGejJxuHG75WWWs",
+            "provider" => "twitter",
+            "state" => Jason.encode!(state_params)
+          }
+        )
+
+      assert html_response(conn, 302)
+      assert redirected_to(conn) == app.redirect_uris
+      assert get_flash(conn, :error) == "Failed to authenticate: (error description)."
+    end
+
+    test "GET /oauth/registration_details renders registration details form", %{
+      app: app,
+      conn: conn
+    } do
+      conn =
+        get(
+          conn,
+          "/oauth/registration_details",
+          %{
+            "authorization" => %{
+              "scopes" => app.scopes,
+              "client_id" => app.client_id,
+              "redirect_uri" => OAuthController.default_redirect_uri(app),
+              "state" => "a_state",
+              "nickname" => nil,
+              "email" => "john@doe.com"
+            }
+          }
+        )
+
+      assert response = html_response(conn, 200)
+      assert response =~ ~r/name="op" type="submit" value="register"/
+      assert response =~ ~r/name="op" type="submit" value="connect"/
+    end
+
+    test "with valid params, POST /oauth/register?op=register redirects to `redirect_uri` with `code`",
+         %{
+           app: app,
+           conn: conn
+         } do
+      registration = insert(:registration, user: nil, info: %{"nickname" => nil, "email" => nil})
+      redirect_uri = OAuthController.default_redirect_uri(app)
+
+      conn =
+        conn
+        |> put_session(:registration_id, registration.id)
+        |> post(
+          "/oauth/register",
+          %{
+            "op" => "register",
+            "authorization" => %{
+              "scopes" => app.scopes,
+              "client_id" => app.client_id,
+              "redirect_uri" => redirect_uri,
+              "state" => "a_state",
+              "nickname" => "availablenick",
+              "email" => "available@email.com"
+            }
+          }
+        )
+
+      assert html_response(conn, 302)
+      assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
+    end
+
+    test "with unlisted `redirect_uri`, POST /oauth/register?op=register results in HTTP 401",
+         %{
+           app: app,
+           conn: conn
+         } do
+      registration = insert(:registration, user: nil, info: %{"nickname" => nil, "email" => nil})
+      unlisted_redirect_uri = "http://cross-site-request.com"
+
+      conn =
+        conn
+        |> put_session(:registration_id, registration.id)
+        |> post(
+          "/oauth/register",
+          %{
+            "op" => "register",
+            "authorization" => %{
+              "scopes" => app.scopes,
+              "client_id" => app.client_id,
+              "redirect_uri" => unlisted_redirect_uri,
+              "state" => "a_state",
+              "nickname" => "availablenick",
+              "email" => "available@email.com"
+            }
+          }
+        )
+
+      assert html_response(conn, 401)
+    end
+
+    test "with invalid params, POST /oauth/register?op=register renders registration_details page",
+         %{
+           app: app,
+           conn: conn
+         } do
+      another_user = insert(:user)
+      registration = insert(:registration, user: nil, info: %{"nickname" => nil, "email" => nil})
+
+      params = %{
+        "op" => "register",
+        "authorization" => %{
+          "scopes" => app.scopes,
+          "client_id" => app.client_id,
+          "redirect_uri" => OAuthController.default_redirect_uri(app),
+          "state" => "a_state",
+          "nickname" => "availablenickname",
+          "email" => "available@email.com"
+        }
+      }
+
+      for {bad_param, bad_param_value} <-
+            [{"nickname", another_user.nickname}, {"email", another_user.email}] do
+        bad_registration_attrs = %{
+          "authorization" => Map.put(params["authorization"], bad_param, bad_param_value)
+        }
+
+        bad_params = Map.merge(params, bad_registration_attrs)
+
+        conn =
+          conn
+          |> put_session(:registration_id, registration.id)
+          |> post("/oauth/register", bad_params)
+
+        assert html_response(conn, 403) =~ ~r/name="op" type="submit" value="register"/
+        assert get_flash(conn, :error) == "Error: #{bad_param} has already been taken."
+      end
+    end
+
+    test "with valid params, POST /oauth/register?op=connect redirects to `redirect_uri` with `code`",
+         %{
+           app: app,
+           conn: conn
+         } do
+      user = insert(:user, password_hash: Pleroma.Password.Pbkdf2.hash_pwd_salt("testpassword"))
+      registration = insert(:registration, user: nil)
+      redirect_uri = OAuthController.default_redirect_uri(app)
+
+      conn =
+        conn
+        |> put_session(:registration_id, registration.id)
+        |> post(
+          "/oauth/register",
+          %{
+            "op" => "connect",
+            "authorization" => %{
+              "scopes" => app.scopes,
+              "client_id" => app.client_id,
+              "redirect_uri" => redirect_uri,
+              "state" => "a_state",
+              "name" => user.nickname,
+              "password" => "testpassword"
+            }
+          }
+        )
+
+      assert html_response(conn, 302)
+      assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
+    end
+
+    test "with unlisted `redirect_uri`, POST /oauth/register?op=connect results in HTTP 401`",
+         %{
+           app: app,
+           conn: conn
+         } do
+      user = insert(:user, password_hash: Pleroma.Password.Pbkdf2.hash_pwd_salt("testpassword"))
+      registration = insert(:registration, user: nil)
+      unlisted_redirect_uri = "http://cross-site-request.com"
+
+      conn =
+        conn
+        |> put_session(:registration_id, registration.id)
+        |> post(
+          "/oauth/register",
+          %{
+            "op" => "connect",
+            "authorization" => %{
+              "scopes" => app.scopes,
+              "client_id" => app.client_id,
+              "redirect_uri" => unlisted_redirect_uri,
+              "state" => "a_state",
+              "name" => user.nickname,
+              "password" => "testpassword"
+            }
+          }
+        )
+
+      assert html_response(conn, 401)
+    end
+
+    test "with invalid params, POST /oauth/register?op=connect renders registration_details page",
+         %{
+           app: app,
+           conn: conn
+         } do
+      user = insert(:user)
+      registration = insert(:registration, user: nil)
+
+      params = %{
+        "op" => "connect",
+        "authorization" => %{
+          "scopes" => app.scopes,
+          "client_id" => app.client_id,
+          "redirect_uri" => OAuthController.default_redirect_uri(app),
+          "state" => "a_state",
+          "name" => user.nickname,
+          "password" => "wrong password"
+        }
+      }
+
+      conn =
+        conn
+        |> put_session(:registration_id, registration.id)
+        |> post("/oauth/register", params)
+
+      assert html_response(conn, 401) =~ ~r/name="op" type="submit" value="connect"/
+      assert get_flash(conn, :error) == "Invalid Username/Password"
+    end
+  end
+
+  describe "POST /oauth/authorize_callback" do
+    test "redirects with oauth authorization, " <>
+           "granting requested app-supported scopes to both admin- and non-admin users" do
+      app_scopes = ["read", "write", "admin", "secret_scope"]
+      app = insert(:oauth_app, scopes: app_scopes)
+      redirect_uri = OAuthController.default_redirect_uri(app)
+
+      non_admin = insert(:user, is_admin: false)
+      admin = insert(:user, is_admin: true)
+      scopes_subset = ["read:subscope", "write", "admin"]
+
+      # In case scope param is missing, expecting _all_ app-supported scopes to be granted
+      for user <- [non_admin, admin],
+          {requested_scopes, expected_scopes} <-
+            %{scopes_subset => scopes_subset, nil: app_scopes} do
+        conn =
+          post(
+            build_conn(),
+            "/oauth/authorize_callback",
+            %{
+              "authorization" => %{
+                "name" => user.nickname,
+                "password" => "test",
+                "client_id" => app.client_id,
+                "redirect_uri" => redirect_uri,
+                "scope" => requested_scopes,
+                "state" => "statepassed"
+              }
+            }
+          )
+
+        target = redirected_to(conn)
+        assert target =~ redirect_uri
+
+        query = URI.parse(target).query |> URI.query_decoder() |> Map.new()
+
+        assert %{"state" => "statepassed", "code" => code} = query
+        auth = Repo.get_by(Authorization, token: code)
+        assert auth
+        assert auth.scopes == expected_scopes
+      end
+    end
+
+    test "authorize from cookie" do
+      user = insert(:user)
+      app = insert(:oauth_app)
+      oauth_token = insert(:oauth_token, user: user, app: app)
+      redirect_uri = OAuthController.default_redirect_uri(app)
+
+      conn =
+        build_conn()
+        |> Plug.Session.call(Plug.Session.init(@session_opts))
+        |> fetch_session()
+        |> AuthHelper.put_session_token(oauth_token.token)
+        |> post(
+          "/oauth/authorize_callback",
+          %{
+            "authorization" => %{
+              "name" => user.nickname,
+              "client_id" => app.client_id,
+              "redirect_uri" => redirect_uri,
+              "scope" => app.scopes,
+              "state" => "statepassed"
+            }
+          }
+        )
+
+      target = redirected_to(conn)
+      assert target =~ redirect_uri
+
+      query = URI.parse(target).query |> URI.query_decoder() |> Map.new()
+
+      assert %{"state" => "statepassed", "code" => code} = query
+      auth = Repo.get_by(Authorization, token: code)
+      assert auth
+      assert auth.scopes == app.scopes
+    end
+
+    test "redirect to on two-factor auth page" do
+      otp_secret = TOTP.generate_secret()
+
+      user =
+        insert(:user,
+          multi_factor_authentication_settings: %MFA.Settings{
+            enabled: true,
+            totp: %MFA.Settings.TOTP{secret: otp_secret, confirmed: true}
+          }
+        )
+
+      app = insert(:oauth_app, scopes: ["read", "write", "follow"])
+
+      conn =
+        build_conn()
+        |> post("/oauth/authorize_callback", %{
+          "authorization" => %{
+            "name" => user.nickname,
+            "password" => "test",
+            "client_id" => app.client_id,
+            "redirect_uri" => app.redirect_uris,
+            "scope" => "read write",
+            "state" => "statepassed"
+          }
+        })
+
+      result = html_response(conn, 200)
+
+      mfa_token = Repo.get_by(MFA.Token, user_id: user.id)
+      assert result =~ app.redirect_uris
+      assert result =~ "statepassed"
+      assert result =~ mfa_token.token
+      assert result =~ "Two-factor authentication"
+    end
+
+    test "returns 401 for wrong credentials", %{conn: conn} do
+      user = insert(:user)
+      app = insert(:oauth_app)
+      redirect_uri = OAuthController.default_redirect_uri(app)
+
+      result =
+        conn
+        |> post("/oauth/authorize_callback", %{
+          "authorization" => %{
+            "name" => user.nickname,
+            "password" => "wrong",
+            "client_id" => app.client_id,
+            "redirect_uri" => redirect_uri,
+            "state" => "statepassed",
+            "scope" => Enum.join(app.scopes, " ")
+          }
+        })
+        |> html_response(:unauthorized)
+
+      # Keep the details
+      assert result =~ app.client_id
+      assert result =~ redirect_uri
+
+      # Error message
+      assert result =~ "Invalid Username/Password"
+    end
+
+    test "returns 401 for missing scopes" do
+      user = insert(:user, is_admin: false)
+      app = insert(:oauth_app, scopes: ["read", "write", "admin"])
+      redirect_uri = OAuthController.default_redirect_uri(app)
+
+      result =
+        build_conn()
+        |> post("/oauth/authorize_callback", %{
+          "authorization" => %{
+            "name" => user.nickname,
+            "password" => "test",
+            "client_id" => app.client_id,
+            "redirect_uri" => redirect_uri,
+            "state" => "statepassed",
+            "scope" => ""
+          }
+        })
+        |> html_response(:unauthorized)
+
+      # Keep the details
+      assert result =~ app.client_id
+      assert result =~ redirect_uri
+
+      # Error message
+      assert result =~ "This action is outside the authorized scopes"
+    end
+
+    test "returns 401 for scopes beyond app scopes hierarchy", %{conn: conn} do
+      user = insert(:user)
+      app = insert(:oauth_app, scopes: ["read", "write"])
+      redirect_uri = OAuthController.default_redirect_uri(app)
+
+      result =
+        conn
+        |> post("/oauth/authorize_callback", %{
+          "authorization" => %{
+            "name" => user.nickname,
+            "password" => "test",
+            "client_id" => app.client_id,
+            "redirect_uri" => redirect_uri,
+            "state" => "statepassed",
+            "scope" => "read write follow"
+          }
+        })
+        |> html_response(:unauthorized)
+
+      # Keep the details
+      assert result =~ app.client_id
+      assert result =~ redirect_uri
+
+      # Error message
+      assert result =~ "This action is outside the authorized scopes"
+    end
+  end
+end
diff --git a/test/pleroma/web/o_auth/o_auth_controller_test.exs b/test/pleroma/web/o_auth/o_auth_controller_test.exs
index c0f243a75..4e51edb63 100644
--- a/test/pleroma/web/o_auth/o_auth_controller_test.exs
+++ b/test/pleroma/web/o_auth/o_auth_controller_test.exs
@@ -59,708 +59,6 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
       assert response =~ "Sign in with Twitter"
       assert response =~ o_auth_path(conn, :prepare_request)
     end
-
-    test "GET /oauth/prepare_request encodes parameters as `state` and redirects", %{
-      app: app,
-      conn: conn
-    } do
-      conn =
-        get(
-          conn,
-          "/oauth/prepare_request",
-          %{
-            "provider" => "twitter",
-            "authorization" => %{
-              "scope" => "read follow",
-              "client_id" => app.client_id,
-              "redirect_uri" => OAuthController.default_redirect_uri(app),
-              "state" => "a_state"
-            }
-          }
-        )
-
-      assert html_response(conn, 302)
-
-      redirect_query = URI.parse(redirected_to(conn)).query
-      assert %{"state" => state_param} = URI.decode_query(redirect_query)
-      assert {:ok, state_components} = Jason.decode(state_param)
-
-      expected_client_id = app.client_id
-      expected_redirect_uri = app.redirect_uris
-
-      assert %{
-               "scope" => "read follow",
-               "client_id" => ^expected_client_id,
-               "redirect_uri" => ^expected_redirect_uri,
-               "state" => "a_state"
-             } = state_components
-    end
-
-    test "with user-bound registration, GET /oauth/<provider>/callback redirects to `redirect_uri` with `code`",
-         %{app: app, conn: conn} do
-      registration = insert(:registration)
-      redirect_uri = OAuthController.default_redirect_uri(app)
-
-      state_params = %{
-        "scope" => Enum.join(app.scopes, " "),
-        "client_id" => app.client_id,
-        "redirect_uri" => redirect_uri,
-        "state" => ""
-      }
-
-      conn =
-        conn
-        |> assign(:ueberauth_auth, %{provider: registration.provider, uid: registration.uid})
-        |> get(
-          "/oauth/twitter/callback",
-          %{
-            "oauth_token" => "G-5a3AAAAAAAwMH9AAABaektfSM",
-            "oauth_verifier" => "QZl8vUqNvXMTKpdmUnGejJxuHG75WWWs",
-            "provider" => "twitter",
-            "state" => Jason.encode!(state_params)
-          }
-        )
-
-      assert html_response(conn, 302)
-      assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
-    end
-
-    test "with user-unbound registration, GET /oauth/<provider>/callback renders registration_details page",
-         %{app: app, conn: conn} do
-      user = insert(:user)
-
-      state_params = %{
-        "scope" => "read write",
-        "client_id" => app.client_id,
-        "redirect_uri" => OAuthController.default_redirect_uri(app),
-        "state" => "a_state"
-      }
-
-      conn =
-        conn
-        |> assign(:ueberauth_auth, %{
-          provider: "twitter",
-          uid: "171799000",
-          info: %{nickname: user.nickname, email: user.email, name: user.name, description: nil}
-        })
-        |> get(
-          "/oauth/twitter/callback",
-          %{
-            "oauth_token" => "G-5a3AAAAAAAwMH9AAABaektfSM",
-            "oauth_verifier" => "QZl8vUqNvXMTKpdmUnGejJxuHG75WWWs",
-            "provider" => "twitter",
-            "state" => Jason.encode!(state_params)
-          }
-        )
-
-      assert response = html_response(conn, 200)
-      assert response =~ ~r/name="op" type="submit" value="register"/
-      assert response =~ ~r/name="op" type="submit" value="connect"/
-      assert response =~ user.email
-      assert response =~ user.nickname
-    end
-
-    test "on authentication error, GET /oauth/<provider>/callback redirects to `redirect_uri`", %{
-      app: app,
-      conn: conn
-    } do
-      state_params = %{
-        "scope" => Enum.join(app.scopes, " "),
-        "client_id" => app.client_id,
-        "redirect_uri" => OAuthController.default_redirect_uri(app),
-        "state" => ""
-      }
-
-      conn =
-        conn
-        |> assign(:ueberauth_failure, %{errors: [%{message: "(error description)"}]})
-        |> get(
-          "/oauth/twitter/callback",
-          %{
-            "oauth_token" => "G-5a3AAAAAAAwMH9AAABaektfSM",
-            "oauth_verifier" => "QZl8vUqNvXMTKpdmUnGejJxuHG75WWWs",
-            "provider" => "twitter",
-            "state" => Jason.encode!(state_params)
-          }
-        )
-
-      assert html_response(conn, 302)
-      assert redirected_to(conn) == app.redirect_uris
-      assert get_flash(conn, :error) == "Failed to authenticate: (error description)."
-    end
-
-    test "GET /oauth/registration_details renders registration details form", %{
-      app: app,
-      conn: conn
-    } do
-      conn =
-        get(
-          conn,
-          "/oauth/registration_details",
-          %{
-            "authorization" => %{
-              "scopes" => app.scopes,
-              "client_id" => app.client_id,
-              "redirect_uri" => OAuthController.default_redirect_uri(app),
-              "state" => "a_state",
-              "nickname" => nil,
-              "email" => "john@doe.com"
-            }
-          }
-        )
-
-      assert response = html_response(conn, 200)
-      assert response =~ ~r/name="op" type="submit" value="register"/
-      assert response =~ ~r/name="op" type="submit" value="connect"/
-    end
-
-    test "with valid params, POST /oauth/register?op=register redirects to `redirect_uri` with `code`",
-         %{
-           app: app,
-           conn: conn
-         } do
-      registration = insert(:registration, user: nil, info: %{"nickname" => nil, "email" => nil})
-      redirect_uri = OAuthController.default_redirect_uri(app)
-
-      conn =
-        conn
-        |> put_session(:registration_id, registration.id)
-        |> post(
-          "/oauth/register",
-          %{
-            "op" => "register",
-            "authorization" => %{
-              "scopes" => app.scopes,
-              "client_id" => app.client_id,
-              "redirect_uri" => redirect_uri,
-              "state" => "a_state",
-              "nickname" => "availablenick",
-              "email" => "available@email.com"
-            }
-          }
-        )
-
-      assert html_response(conn, 302)
-      assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
-    end
-
-    test "with unlisted `redirect_uri`, POST /oauth/register?op=register results in HTTP 401",
-         %{
-           app: app,
-           conn: conn
-         } do
-      registration = insert(:registration, user: nil, info: %{"nickname" => nil, "email" => nil})
-      unlisted_redirect_uri = "http://cross-site-request.com"
-
-      conn =
-        conn
-        |> put_session(:registration_id, registration.id)
-        |> post(
-          "/oauth/register",
-          %{
-            "op" => "register",
-            "authorization" => %{
-              "scopes" => app.scopes,
-              "client_id" => app.client_id,
-              "redirect_uri" => unlisted_redirect_uri,
-              "state" => "a_state",
-              "nickname" => "availablenick",
-              "email" => "available@email.com"
-            }
-          }
-        )
-
-      assert html_response(conn, 401)
-    end
-
-    test "with invalid params, POST /oauth/register?op=register renders registration_details page",
-         %{
-           app: app,
-           conn: conn
-         } do
-      another_user = insert(:user)
-      registration = insert(:registration, user: nil, info: %{"nickname" => nil, "email" => nil})
-
-      params = %{
-        "op" => "register",
-        "authorization" => %{
-          "scopes" => app.scopes,
-          "client_id" => app.client_id,
-          "redirect_uri" => OAuthController.default_redirect_uri(app),
-          "state" => "a_state",
-          "nickname" => "availablenickname",
-          "email" => "available@email.com"
-        }
-      }
-
-      for {bad_param, bad_param_value} <-
-            [{"nickname", another_user.nickname}, {"email", another_user.email}] do
-        bad_registration_attrs = %{
-          "authorization" => Map.put(params["authorization"], bad_param, bad_param_value)
-        }
-
-        bad_params = Map.merge(params, bad_registration_attrs)
-
-        conn =
-          conn
-          |> put_session(:registration_id, registration.id)
-          |> post("/oauth/register", bad_params)
-
-        assert html_response(conn, 403) =~ ~r/name="op" type="submit" value="register"/
-        assert get_flash(conn, :error) == "Error: #{bad_param} has already been taken."
-      end
-    end
-
-    test "with valid params, POST /oauth/register?op=connect redirects to `redirect_uri` with `code`",
-         %{
-           app: app,
-           conn: conn
-         } do
-      user = insert(:user, password_hash: Pleroma.Password.Pbkdf2.hash_pwd_salt("testpassword"))
-      registration = insert(:registration, user: nil)
-      redirect_uri = OAuthController.default_redirect_uri(app)
-
-      conn =
-        conn
-        |> put_session(:registration_id, registration.id)
-        |> post(
-          "/oauth/register",
-          %{
-            "op" => "connect",
-            "authorization" => %{
-              "scopes" => app.scopes,
-              "client_id" => app.client_id,
-              "redirect_uri" => redirect_uri,
-              "state" => "a_state",
-              "name" => user.nickname,
-              "password" => "testpassword"
-            }
-          }
-        )
-
-      assert html_response(conn, 302)
-      assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
-    end
-
-    test "with unlisted `redirect_uri`, POST /oauth/register?op=connect results in HTTP 401`",
-         %{
-           app: app,
-           conn: conn
-         } do
-      user = insert(:user, password_hash: Pleroma.Password.Pbkdf2.hash_pwd_salt("testpassword"))
-      registration = insert(:registration, user: nil)
-      unlisted_redirect_uri = "http://cross-site-request.com"
-
-      conn =
-        conn
-        |> put_session(:registration_id, registration.id)
-        |> post(
-          "/oauth/register",
-          %{
-            "op" => "connect",
-            "authorization" => %{
-              "scopes" => app.scopes,
-              "client_id" => app.client_id,
-              "redirect_uri" => unlisted_redirect_uri,
-              "state" => "a_state",
-              "name" => user.nickname,
-              "password" => "testpassword"
-            }
-          }
-        )
-
-      assert html_response(conn, 401)
-    end
-
-    test "with invalid params, POST /oauth/register?op=connect renders registration_details page",
-         %{
-           app: app,
-           conn: conn
-         } do
-      user = insert(:user)
-      registration = insert(:registration, user: nil)
-
-      params = %{
-        "op" => "connect",
-        "authorization" => %{
-          "scopes" => app.scopes,
-          "client_id" => app.client_id,
-          "redirect_uri" => OAuthController.default_redirect_uri(app),
-          "state" => "a_state",
-          "name" => user.nickname,
-          "password" => "wrong password"
-        }
-      }
-
-      conn =
-        conn
-        |> put_session(:registration_id, registration.id)
-        |> post("/oauth/register", params)
-
-      assert html_response(conn, 401) =~ ~r/name="op" type="submit" value="connect"/
-      assert get_flash(conn, :error) == "Invalid Username/Password"
-    end
-  end
-
-  describe "GET /oauth/authorize" do
-    setup do
-      [
-        app: insert(:oauth_app, redirect_uris: "https://redirect.url"),
-        conn:
-          build_conn()
-          |> Plug.Session.call(Plug.Session.init(@session_opts))
-          |> fetch_session()
-      ]
-    end
-
-    test "renders authentication page", %{app: app, conn: conn} do
-      conn =
-        get(
-          conn,
-          "/oauth/authorize",
-          %{
-            "response_type" => "code",
-            "client_id" => app.client_id,
-            "redirect_uri" => OAuthController.default_redirect_uri(app),
-            "scope" => "read"
-          }
-        )
-
-      assert html_response(conn, 200) =~ ~s(type="submit")
-    end
-
-    test "properly handles internal calls with `authorization`-wrapped params", %{
-      app: app,
-      conn: conn
-    } do
-      conn =
-        get(
-          conn,
-          "/oauth/authorize",
-          %{
-            "authorization" => %{
-              "response_type" => "code",
-              "client_id" => app.client_id,
-              "redirect_uri" => OAuthController.default_redirect_uri(app),
-              "scope" => "read"
-            }
-          }
-        )
-
-      assert html_response(conn, 200) =~ ~s(type="submit")
-    end
-
-    test "renders authentication page if user is already authenticated but `force_login` is tru-ish",
-         %{app: app, conn: conn} do
-      token = insert(:oauth_token, app: app)
-
-      conn =
-        conn
-        |> AuthHelper.put_session_token(token.token)
-        |> get(
-          "/oauth/authorize",
-          %{
-            "response_type" => "code",
-            "client_id" => app.client_id,
-            "redirect_uri" => OAuthController.default_redirect_uri(app),
-            "scope" => "read",
-            "force_login" => "true"
-          }
-        )
-
-      assert html_response(conn, 200) =~ ~s(type="submit")
-    end
-
-    test "renders authentication page if user is already authenticated but user request with another client",
-         %{
-           app: app,
-           conn: conn
-         } do
-      token = insert(:oauth_token, app: app)
-
-      conn =
-        conn
-        |> AuthHelper.put_session_token(token.token)
-        |> get(
-          "/oauth/authorize",
-          %{
-            "response_type" => "code",
-            "client_id" => "another_client_id",
-            "redirect_uri" => OAuthController.default_redirect_uri(app),
-            "scope" => "read"
-          }
-        )
-
-      assert html_response(conn, 200) =~ ~s(type="submit")
-    end
-
-    test "with existing authentication and non-OOB `redirect_uri`, redirects to app with `token` and `state` params",
-         %{
-           app: app,
-           conn: conn
-         } do
-      token = insert(:oauth_token, app: app)
-
-      conn =
-        conn
-        |> AuthHelper.put_session_token(token.token)
-        |> get(
-          "/oauth/authorize",
-          %{
-            "response_type" => "code",
-            "client_id" => app.client_id,
-            "redirect_uri" => OAuthController.default_redirect_uri(app),
-            "state" => "specific_client_state",
-            "scope" => "read"
-          }
-        )
-
-      assert URI.decode(redirected_to(conn)) ==
-               "https://redirect.url?access_token=#{token.token}&state=specific_client_state"
-    end
-
-    test "with existing authentication and unlisted non-OOB `redirect_uri`, redirects without credentials",
-         %{
-           app: app,
-           conn: conn
-         } do
-      unlisted_redirect_uri = "http://cross-site-request.com"
-      token = insert(:oauth_token, app: app)
-
-      conn =
-        conn
-        |> AuthHelper.put_session_token(token.token)
-        |> get(
-          "/oauth/authorize",
-          %{
-            "response_type" => "code",
-            "client_id" => app.client_id,
-            "redirect_uri" => unlisted_redirect_uri,
-            "state" => "specific_client_state",
-            "scope" => "read"
-          }
-        )
-
-      assert redirected_to(conn) == unlisted_redirect_uri
-    end
-
-    test "with existing authentication and OOB `redirect_uri`, redirects to app with `token` and `state` params",
-         %{
-           app: app,
-           conn: conn
-         } do
-      token = insert(:oauth_token, app: app)
-
-      conn =
-        conn
-        |> AuthHelper.put_session_token(token.token)
-        |> get(
-          "/oauth/authorize",
-          %{
-            "response_type" => "code",
-            "client_id" => app.client_id,
-            "redirect_uri" => "urn:ietf:wg:oauth:2.0:oob",
-            "scope" => "read"
-          }
-        )
-
-      assert html_response(conn, 200) =~ "Authorization exists"
-    end
-  end
-
-  describe "POST /oauth/authorize" do
-    test "redirects with oauth authorization, " <>
-           "granting requested app-supported scopes to both admin- and non-admin users" do
-      app_scopes = ["read", "write", "admin", "secret_scope"]
-      app = insert(:oauth_app, scopes: app_scopes)
-      redirect_uri = OAuthController.default_redirect_uri(app)
-
-      non_admin = insert(:user, is_admin: false)
-      admin = insert(:user, is_admin: true)
-      scopes_subset = ["read:subscope", "write", "admin"]
-
-      # In case scope param is missing, expecting _all_ app-supported scopes to be granted
-      for user <- [non_admin, admin],
-          {requested_scopes, expected_scopes} <-
-            %{scopes_subset => scopes_subset, nil: app_scopes} do
-        conn =
-          post(
-            build_conn(),
-            "/oauth/authorize",
-            %{
-              "authorization" => %{
-                "name" => user.nickname,
-                "password" => "test",
-                "client_id" => app.client_id,
-                "redirect_uri" => redirect_uri,
-                "scope" => requested_scopes,
-                "state" => "statepassed"
-              }
-            }
-          )
-
-        target = redirected_to(conn)
-        assert target =~ redirect_uri
-
-        query = URI.parse(target).query |> URI.query_decoder() |> Map.new()
-
-        assert %{"state" => "statepassed", "code" => code} = query
-        auth = Repo.get_by(Authorization, token: code)
-        assert auth
-        assert auth.scopes == expected_scopes
-      end
-    end
-
-    test "authorize from cookie" do
-      user = insert(:user)
-      app = insert(:oauth_app)
-      oauth_token = insert(:oauth_token, user: user, app: app)
-      redirect_uri = OAuthController.default_redirect_uri(app)
-
-      conn =
-        build_conn()
-        |> Plug.Session.call(Plug.Session.init(@session_opts))
-        |> fetch_session()
-        |> AuthHelper.put_session_token(oauth_token.token)
-        |> post(
-          "/oauth/authorize",
-          %{
-            "authorization" => %{
-              "name" => user.nickname,
-              "client_id" => app.client_id,
-              "redirect_uri" => redirect_uri,
-              "scope" => app.scopes,
-              "state" => "statepassed"
-            }
-          }
-        )
-
-      target = redirected_to(conn)
-      assert target =~ redirect_uri
-
-      query = URI.parse(target).query |> URI.query_decoder() |> Map.new()
-
-      assert %{"state" => "statepassed", "code" => code} = query
-      auth = Repo.get_by(Authorization, token: code)
-      assert auth
-      assert auth.scopes == app.scopes
-    end
-
-    test "redirect to on two-factor auth page" do
-      otp_secret = TOTP.generate_secret()
-
-      user =
-        insert(:user,
-          multi_factor_authentication_settings: %MFA.Settings{
-            enabled: true,
-            totp: %MFA.Settings.TOTP{secret: otp_secret, confirmed: true}
-          }
-        )
-
-      app = insert(:oauth_app, scopes: ["read", "write", "follow"])
-
-      conn =
-        build_conn()
-        |> post("/oauth/authorize", %{
-          "authorization" => %{
-            "name" => user.nickname,
-            "password" => "test",
-            "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
-            "scope" => "read write",
-            "state" => "statepassed"
-          }
-        })
-
-      result = html_response(conn, 200)
-
-      mfa_token = Repo.get_by(MFA.Token, user_id: user.id)
-      assert result =~ app.redirect_uris
-      assert result =~ "statepassed"
-      assert result =~ mfa_token.token
-      assert result =~ "Two-factor authentication"
-    end
-
-    test "returns 401 for wrong credentials", %{conn: conn} do
-      user = insert(:user)
-      app = insert(:oauth_app)
-      redirect_uri = OAuthController.default_redirect_uri(app)
-
-      result =
-        conn
-        |> post("/oauth/authorize", %{
-          "authorization" => %{
-            "name" => user.nickname,
-            "password" => "wrong",
-            "client_id" => app.client_id,
-            "redirect_uri" => redirect_uri,
-            "state" => "statepassed",
-            "scope" => Enum.join(app.scopes, " ")
-          }
-        })
-        |> html_response(:unauthorized)
-
-      # Keep the details
-      assert result =~ app.client_id
-      assert result =~ redirect_uri
-
-      # Error message
-      assert result =~ "Invalid Username/Password"
-    end
-
-    test "returns 401 for missing scopes" do
-      user = insert(:user, is_admin: false)
-      app = insert(:oauth_app, scopes: ["read", "write", "admin"])
-      redirect_uri = OAuthController.default_redirect_uri(app)
-
-      result =
-        build_conn()
-        |> post("/oauth/authorize", %{
-          "authorization" => %{
-            "name" => user.nickname,
-            "password" => "test",
-            "client_id" => app.client_id,
-            "redirect_uri" => redirect_uri,
-            "state" => "statepassed",
-            "scope" => ""
-          }
-        })
-        |> html_response(:unauthorized)
-
-      # Keep the details
-      assert result =~ app.client_id
-      assert result =~ redirect_uri
-
-      # Error message
-      assert result =~ "This action is outside the authorized scopes"
-    end
-
-    test "returns 401 for scopes beyond app scopes hierarchy", %{conn: conn} do
-      user = insert(:user)
-      app = insert(:oauth_app, scopes: ["read", "write"])
-      redirect_uri = OAuthController.default_redirect_uri(app)
-
-      result =
-        conn
-        |> post("/oauth/authorize", %{
-          "authorization" => %{
-            "name" => user.nickname,
-            "password" => "test",
-            "client_id" => app.client_id,
-            "redirect_uri" => redirect_uri,
-            "state" => "statepassed",
-            "scope" => "read write follow"
-          }
-        })
-        |> html_response(:unauthorized)
-
-      # Keep the details
-      assert result =~ app.client_id
-      assert result =~ redirect_uri
-
-      # Error message
-      assert result =~ "This action is outside the authorized scopes"
-    end
   end
 
   describe "POST /oauth/token" do
@@ -1136,12 +434,16 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
 
       response =
         build_conn()
-        |> post("/oauth/token", %{
-          "grant_type" => "refresh_token",
-          "refresh_token" => token.refresh_token,
-          "client_id" => app.client_id,
-          "client_secret" => app.client_secret
-        })
+        |> post(
+          "/oauth/token?#{
+            URI.encode_query(%{
+              "grant_type" => "refresh_token",
+              "refresh_token" => token.refresh_token,
+              "client_id" => app.client_id,
+              "client_secret" => app.client_secret
+            })
+          }"
+        )
         |> json_response_and_validate_schema(200)
 
       ap_id = user.ap_id
@@ -1174,12 +476,16 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
 
       response =
         build_conn()
-        |> post("/oauth/token", %{
-          "grant_type" => "refresh_token",
-          "refresh_token" => token.token,
-          "client_id" => app.client_id,
-          "client_secret" => app.client_secret
-        })
+        |> post(
+          "/oauth/token?#{
+            URI.encode_query(%{
+              "grant_type" => "refresh_token",
+              "refresh_token" => token.token,
+              "client_id" => app.client_id,
+              "client_secret" => app.client_secret
+            })
+          }"
+        )
         |> json_response_and_validate_schema(400)
 
       assert %{"error" => "Invalid credentials"} == response
@@ -1190,12 +496,16 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
 
       response =
         build_conn()
-        |> post("/oauth/token", %{
-          "grant_type" => "refresh_token",
-          "refresh_token" => "token.refresh_token",
-          "client_id" => app.client_id,
-          "client_secret" => app.client_secret
-        })
+        |> post(
+          "/oauth/token?#{
+            URI.encode_query(%{
+              "grant_type" => "refresh_token",
+              "refresh_token" => "token.refresh_token",
+              "client_id" => app.client_id,
+              "client_secret" => app.client_secret
+            })
+          }"
+        )
         |> json_response_and_validate_schema(400)
 
       assert %{"error" => "Invalid credentials"} == response
@@ -1218,12 +528,16 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
 
       response =
         build_conn()
-        |> post("/oauth/token", %{
-          "grant_type" => "refresh_token",
-          "refresh_token" => access_token.refresh_token,
-          "client_id" => app.client_id,
-          "client_secret" => app.client_secret
-        })
+        |> post(
+          "/oauth/token?#{
+            URI.encode_query(%{
+              "grant_type" => "refresh_token",
+              "refresh_token" => access_token.refresh_token,
+              "client_id" => app.client_id,
+              "client_secret" => app.client_secret
+            })
+          }"
+        )
         |> json_response_and_validate_schema(200)
 
       ap_id = user.ap_id
@@ -1304,4 +618,170 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
       assert %{"error" => "Bad request"} == response
     end
   end
+
+  describe "GET /oauth/authorize" do
+    setup do
+      [
+        app: insert(:oauth_app, redirect_uris: "https://redirect.url"),
+        conn:
+          build_conn()
+          |> Plug.Session.call(Plug.Session.init(@session_opts))
+          |> fetch_session()
+      ]
+    end
+
+    test "renders authentication page", %{app: app, conn: conn} do
+      conn =
+        get(
+          conn,
+          "/oauth/authorize",
+          %{
+            "response_type" => "code",
+            "client_id" => app.client_id,
+            "redirect_uri" => OAuthController.default_redirect_uri(app),
+            "scope" => "read"
+          }
+        )
+
+      assert html_response(conn, 200) =~ ~s(type="submit")
+    end
+
+    test "properly handles internal calls with `authorization`-wrapped params", %{
+      app: app,
+      conn: conn
+    } do
+      conn =
+        get(
+          conn,
+          "/oauth/authorize",
+          %{
+            "authorization" => %{
+              "response_type" => "code",
+              "client_id" => app.client_id,
+              "redirect_uri" => OAuthController.default_redirect_uri(app),
+              "scope" => "read"
+            }
+          }
+        )
+
+      assert html_response(conn, 200) =~ ~s(type="submit")
+    end
+
+    test "renders authentication page if user is already authenticated but `force_login` is tru-ish",
+         %{app: app, conn: conn} do
+      token = insert(:oauth_token, app: app)
+
+      conn =
+        conn
+        |> AuthHelper.put_session_token(token.token)
+        |> get(
+          "/oauth/authorize",
+          %{
+            "response_type" => "code",
+            "client_id" => app.client_id,
+            "redirect_uri" => OAuthController.default_redirect_uri(app),
+            "scope" => "read",
+            "force_login" => "true"
+          }
+        )
+
+      assert html_response(conn, 200) =~ ~s(type="submit")
+    end
+
+    test "renders authentication page if user is already authenticated but user request with another client",
+         %{
+           app: app,
+           conn: conn
+         } do
+      token = insert(:oauth_token, app: app)
+
+      conn =
+        conn
+        |> AuthHelper.put_session_token(token.token)
+        |> get(
+          "/oauth/authorize",
+          %{
+            "response_type" => "code",
+            "client_id" => "another_client_id",
+            "redirect_uri" => OAuthController.default_redirect_uri(app),
+            "scope" => "read"
+          }
+        )
+
+      assert html_response(conn, 200) =~ ~s(type="submit")
+    end
+
+    test "with existing authentication and non-OOB `redirect_uri`, redirects to app with `token` and `state` params",
+         %{
+           app: app,
+           conn: conn
+         } do
+      token = insert(:oauth_token, app: app)
+
+      conn =
+        conn
+        |> AuthHelper.put_session_token(token.token)
+        |> get(
+          "/oauth/authorize",
+          %{
+            "response_type" => "code",
+            "client_id" => app.client_id,
+            "redirect_uri" => OAuthController.default_redirect_uri(app),
+            "state" => "specific_client_state",
+            "scope" => "read"
+          }
+        )
+
+      assert URI.decode(redirected_to(conn)) ==
+               "https://redirect.url?access_token=#{token.token}&state=specific_client_state"
+    end
+
+    test "with existing authentication and unlisted non-OOB `redirect_uri`, redirects without credentials",
+         %{
+           app: app,
+           conn: conn
+         } do
+      unlisted_redirect_uri = "http://cross-site-request.com"
+      token = insert(:oauth_token, app: app)
+
+      conn =
+        conn
+        |> AuthHelper.put_session_token(token.token)
+        |> get(
+          "/oauth/authorize",
+          %{
+            "response_type" => "code",
+            "client_id" => app.client_id,
+            "redirect_uri" => unlisted_redirect_uri,
+            "state" => "specific_client_state",
+            "scope" => "read"
+          }
+        )
+
+      assert redirected_to(conn) == unlisted_redirect_uri
+    end
+
+    test "with existing authentication and OOB `redirect_uri`, redirects to app with `token` and `state` params",
+         %{
+           app: app,
+           conn: conn
+         } do
+      token = insert(:oauth_token, app: app)
+
+      conn =
+        conn
+        |> AuthHelper.put_session_token(token.token)
+        |> get(
+          "/oauth/authorize",
+          %{
+            "response_type" => "code",
+            "client_id" => app.client_id,
+            "redirect_uri" => "urn:ietf:wg:oauth:2.0:oob",
+            "scope" => "read"
+          }
+        )
+
+      assert html_response(conn, 200) =~ "Authorization exists"
+    end
+  end
 end