Tweak OAuth lib to respect x-forwarded-proto

Dash's OAuth token requests are signed with an https url, but when
Drupal get them it tries to verify the signature with an http url
because nginx is doing the SSL termination.  This patch makes
Drupal verify with an https url if x-forwarded-proto is https.

Change-Id: I6fd058ff8122ced25eb6aa6c0a03d020c78bf897
Merge "Tweak OAuth lib to respect x-forwarded-proto"