Add log messages to clarify log messages about API CSRF token verification failure

lib/gitlab/request_forgery_protection.rb

@@ -7,6 +7,14 @@ module Gitlab
     class Controller < ActionController::Base
       protect_from_forgery with: :exception
 
+      rescue_from ActionController::InvalidAuthenticityToken do |e|
+        logger.warn "This CSRF token verification failure is handled internally by `GitLab::RequestForgeryProtection`"
+        logger.warn "Unlike the logs may suggest, this does not result in an actual 422 response to the user"
+        logger.warn "For API requests, the only effect is that `current_user` will be `nil` for the duration of the request"
+
+        raise e
+      end
+
       def index
         head :ok
       end