Move OAuth flow tests from feature tests to system tests (#29837)

spec/system/oauth_spec.rb

@@ -3,13 +3,14 @@
 require 'rails_helper'
 
 describe 'Using OAuth from an external app' do
-  let(:client_app) { Doorkeeper::Application.create!(name: 'test', redirect_uri: 'http://localhost/', scopes: 'read') }
+  let(:client_app) { Doorkeeper::Application.create!(name: 'test', redirect_uri: 'http://localhost/health', scopes: 'read') }
 
   context 'when the user is already logged in' do
     let!(:user) { Fabricate(:user) }
 
     before do
-      sign_in user, scope: :user
+      visit new_user_session_path
+      fill_in_auth_details(user.email, user.password)
     end
 
     it 'when accepting the authorization request' do
@@ -164,6 +165,8 @@ describe 'Using OAuth from an external app' do
         expect(Doorkeeper::AccessGrant.exists?(application: client_app, resource_owner_id: user.id)).to be false
       end
     end
+    # TODO: external auth
+  end
 
   private
 
@@ -177,7 +180,4 @@ describe 'Using OAuth from an external app' do
     fill_in 'user_otp_attempt', with: value
     click_on I18n.t('auth.login')
   end
-
-    # TODO: external auth
-  end
 end