I do everything as stated on this page developers.google.com however, the window appears for a split second, and then an error in the console "Claimed origin not in whitelist: (mySiteLink)"
Your web origin in the Google API Console should only include http:// or https:// and then the host name. Make sure you don't have / in the end. The web origin is under the OAuth 2.0 Client ID section in the Console.
I remove the '/' at the end of "Javascript Origins" url and solve. Example: Original that error URL: http://www.example.com/
Changed to URL: http://www.example.com
Problem solved.
来源：https://stackoverflow.com/questions/19975326/google-api-sharing-interactive-posts-error-claimed-origin-not-in-whitelist