Alright. I am aware with the limitation that Endpoints can't be served on a custom domain. However, I am serving my application on the custom domain and calling the endpoints with the *.appspot.com domain.
The whole app used to work being served from appspot, but now that my app on custom domain is calling the endpoints on appspot authentication cookies (which what I am using btw) stopped being sent with the XHR calls.
I tried setting withCredentials in the client side, but now I am getting:
Credentials flag is true, but Access-Control-Allow-Credentials is not "true".
Any idea how to (or if it is possible) to send the cookies with the XHR to the endpoints? Or how to enable Access-Control-Allow-Credentials on Endpoints?