Intermittent ASP.NET oAuth issue with Google, AuthenticationManager.GetExternalIdentityAsync is returning null

Question

I am trying to fix an intermittent issue when using Google as an external login provider.

When attempting to login, the user is redirected back to the login page ra

Answer 1

I believe you should't be using app.UseGoogleAuthentication(); as that's a call which will try to use OpenID 2.0, which has been deprecated.
What you should be using instead is OAuth 2.0 for Login (OpenID Connect).
So:

1. register your app in Google Developers Console
2. enable it to access Google+ API (even though you do not intend to use Google+ directly - it's now used as a mean of authentication)
3. enable ASP.NET Identity's Google authentication this way

app.UseGoogleAuthentication(new GoogleOAuth2AuthenticationOptions()  
{  
    ClientId = "YOUR_CLIENT_ID",  
    ClientSecret = "YOUR_CLIENT_SECRET",  
});