Added functionality to retain URL parameters for login redirects

[brm252]

[bradkovach]

In order to ensure proper parsing/encoding, I would suspect that another nested http_build_query should be implemented to "carry over" any params in this fashion...

'redirect_uri'  => $settings->redirect_uri
     . $_SERVER['QUERY_STRING']
          ? "?" . http_build_query( $_GET )
          : "",

Overall, I am concerned that adding data to the authorization loop might break something. @psignoret would know more about this.