How can I get an external OAuth2 authentication service's error messages?

I am currently learning to use OAuth2 and so I have created a Google account and trying to fiddle around with it.

When the authentication fails, all I seem to get is

GetExternalLogin(provider = "Google", error = "access_denied");

... which is not very verbose.

In Fiddler's session log I found a response explaining in detail what the error was:

HTTP/1.1 403 Forbidden
Vary: X-Origin
Content-Type: application/json; charset=UTF-8
Date: Mon, 09 Nov 2015 12:22:00 GMT
Expires: Mon, 09 Nov 2015 12:22:00 GMT
Cache-Control: private, max-age=0
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Server: GSE
Alternate-Protocol: 443:quic,p=1
Alt-Svc: quic=":443"; p="1"; ma=604800
Accept-Ranges: none
Vary: Origin,Accept-Encoding
Content-Length: 520

{
 "error": {"errors": [
   {"domain": "usageLimits","reason": "accessNotConfigured","message": "Access Not Configured. The API (Google+ API) is not enabled for your project. Please use the Google Developers Console to update your configuration.","extendedHelp": "https://console.developers.google.com"
   }
  ],"code": 403,"message": "Access Not Configured. The API (Google+ API) is not enabled for your project. Please use the Google Developers Console to update your configuration."
 }
}

This error was sent to the Katana middleware.

Is there a callback I can set to be able to evaluate such error message?