[Code] oauth2-server-php as an identity provider

[Bojan Živanović]

My team is responsible for Drupal's client (RP) module.

We have also extended the oauth2-server-php library
(https://github.com/bshaffer/oauth2-server-php) to support OpenID
Connect on the server (identity provider) side (currently a part of
the develop branch).
oauth2-server-php is one of the most popular oauth2 library in the PHP
world right now (38800 installs on packagist), and this allows it to
recommend OpenID Connect to anyone looking to use OAuth2 for login
purposes.
We are in the process of joining the interop, and I would like to
request that you add it to the list on
http://openid.net/developers/libraries/.

Cheers,
Bojan