Google API Scope Changed
We discovered the same issue today. Our solution has been working without any hiccups for the last couple of months.
We solved the issue by updating our original scopes 'profile email' to https://www.googleapis.com/auth/userinfo.email https://www.googleapis.com/auth/userinfo.profile and by doing some minor changes to the code.
When initiating the google_auth_oauthlib.flow client, we previously passed in the scopes in a list with only one item which contained a string in which the scopes were separated by spaces.
google_scopes = 'email profile'
self.flow = Flow.from_client_secrets_file(secret_file, scopes=[google_scopes], state=state)
Now, with the updated scopes, we send in a list where each element is a separate scope.
google_scopes = 'https://www.googleapis.com/auth/userinfo.email https://www.googleapis.com/auth/userinfo.profile'
self.flow = Flow.from_client_secrets_file(secret_file, scopes=google_scopes.split(' '), state=state)
Hope it helps, good luck!