Adding some configuration on URLs

Adding a way to configure multiple middleware at the same time.

Let’s say you want to have both a Facebook and Google+ OAuth2 middle
wares, by default they are both bound to /login.

Now you can specify LoginUrl, CallbackUrl and LogoutUrl for both
middleware, avoiding conflicts.
adding callback after successful login

May serve to check in datastore for existence and saves the token for
later use.
clears session cookie
providing much control to the callback