Add more verbose error message if 2FA required

The previous message was just "2FA required." Let's do more here, and
say it's an authentication failure. Explain why, and let's see if
we can't also garden in a link to the docs for how to do this.

Changelog: changed

app/controllers/concerns/enforces_two_factor_authentication.rb

@@ -10,6 +10,11 @@
 module EnforcesTwoFactorAuthentication
   extend ActiveSupport::Concern
 
+  MFA_HELP_PAGE = Rails.application.routes.url_helpers.help_page_url(
+    'user/profile/account/two_factor_authentication.html',
+    anchor: 'enable-two-factor-authentication'
+  )
+
   included do
     before_action :check_two_factor_requirement, except: [:route_not_found]
 
@@ -26,7 +31,11 @@ module EnforcesTwoFactorAuthentication
     if two_factor_authentication_required? && current_user_requires_two_factor?
       case self
       when GraphqlController
-        render_error("2FA required", status: :unauthorized)
+        render_error(
+          _("Authentication error: enable 2FA in your profile settings to continue using GitLab: %{mfa_help_page}") %
+          { mfa_help_page: MFA_HELP_PAGE },
+          status: :unauthorized
+        )
       else
         redirect_to profile_two_factor_auth_path
       end

locale/gitlab.pot

@@ -5260,6 +5260,9 @@ msgstr ""
 msgid "Authentication Log"
 msgstr ""
 
+msgid "Authentication error: enable 2FA in your profile settings to continue using GitLab: %{mfa_help_page}"
+msgstr ""
+
 msgid "Authentication failed: %{error_message}"
 msgstr ""
 

spec/controllers/graphql_controller_spec.rb

@@ -168,7 +168,12 @@ RSpec.describe GraphqlController do
         post :execute
 
         expect(response).to have_gitlab_http_status(:unauthorized)
-        expect(json_response).to eq({ 'errors' => [{ 'message' => '2FA required' }] })
+
+        expected_message = "Authentication error: " \
+        "enable 2FA in your profile settings to continue using GitLab: %{mfa_help_page}" %
+        { mfa_help_page: EnforcesTwoFactorAuthentication::MFA_HELP_PAGE }
+
+        expect(json_response).to eq({ 'errors' => [{ 'message' => expected_message }] })
       end
     end