Added apereo CAS (#1006)

Author: Ajtak

docs/providers/thirdparty.md

@@ -20,6 +20,7 @@ Gateway | Composer Package | Maintainer
 [42 School](https://github.com/mehdibo/oauth2-fortytwo/) | mehdibo/oauth2-fortytwo | [Mehdi Bounya](https://github.com/mehdibo)
 [Amazon](https://github.com/michaelKaefer/oauth2-amazon/) | michaelkaefer/oauth2-amazon | [Michael Käfer](https://github.com/michaelKaefer)
 [Amazon Cognito](https://github.com/CakeDC/oauth2-cognito/) | cakedc/oauth2-cognito | [Cake Development Corporation](https://github.com/CakeDC)
+[Apereo CAS](https://github.com/ajtak/oauth2-apereo-cas) | ajtak/oauth2-apereo-cas | [Jakub Fridrich](https://github.com/Ajtak)
 [Apple](https://github.com/patrickbussmann/oauth2-apple) | patrickbussmann/oauth2-apple | [Patrick Bußmann](https://github.com/patrickbussmann)
 [Auth0](https://github.com/RiskioFr/oauth2-auth0) | riskio/oauth2-auth0 | [Nicolas Eeckeloo](https://github.com/neeckeloo)
 [Azure Active Directory](https://github.com/thenetworg/oauth2-azure) | thenetworg/oauth2-azure | [Jan Hajek](https://github.com/hajekj)