Update thirdparty.md (#761)

Co-authored-by: Ben Ramsey <[email protected]>

Author: ajibarra

docs/providers/thirdparty.md

@@ -21,6 +21,7 @@ $ composer require [vendor/package-name]
 Gateway | Composer Package | Maintainer
 --- | --- | ---
 [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)
 [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)
 [BASE](https://github.com/w-takumi/oauth2-base) | shippinno/oauth-base | [SHIPPInno Corp.](https://www.shippinno.co.jp/)