Possibly spare 1 URL fetch call during _on_signin

[x1ddos]

I'm thinking to make _get_<provider>_user_info() call optional. This way one could spare a URL fetch call when existing users sign in as their profile data have probably been already stored during some previous logins.

Additionally, this could make it easier for a backend profile fetch instead of doing it during the user facing request.

Would this be a good idea?

[conradwt]

@crhym3 This sounds like a very good idea.

[x1ddos]

I'll try to come up with a CL during this week and post it here for a review.