Thanks to @iterateNZ and @jbbarth for reporting and helping to
troubleshoot the issue.

Added proper implementation of `info`, `extra`, and `credentials` OmniAuth Auth Hashes and made the UID value configurable.

Added a URL parameter that is automatically set to the referrer so that the user will be automatically redirected to the page that triggered the need for authentication.

Laid down the foundation by using `omniauth-facebook` as a guide to the structure of this gem and the old OmniAuth determining what needs to be tested.