Add URL to rejection_message if terms_not_accepted

This change improves the OAuth2 error for when users have not accepted
the Terms of Use by providing users with a URL to the gitlab instance
they should sign into in order to accept the Terms of Use.

Changelog: changed

lib/gitlab/auth/user_access_denied_reason.rb

@@ -15,7 +15,7 @@ module Gitlab
           "Your account is pending approval from your administrator and hence blocked."
         when :terms_not_accepted
           "You (#{@user.to_reference}) must accept the Terms of Service in order to perform this action. "\
-          "Please access GitLab from a web browser to accept these terms."
+          "To accept these terms, please access GitLab from a web browser at #{Gitlab.config.gitlab.url}."
         when :deactivated
           "Your account has been deactivated by your administrator. "\
           "Please log back in from a web browser to reactivate your account at #{Gitlab.config.gitlab.url}"

spec/lib/gitlab/auth/user_access_denied_reason_spec.rb

@@ -26,6 +26,7 @@ RSpec.describe Gitlab::Auth::UserAccessDeniedReason do
 
       it { is_expected.to match /must accept the Terms of Service/ }
       it { is_expected.to include(user.username) }
+      it { is_expected.to include(Gitlab.config.gitlab.url) }
     end
 
     context 'when the user is internal' do