OAuth2 vs SimpleSAMLphp: What are the differences?

Developers describe OAuth2 as "An open standard for access delegation". It is an authorization framework that enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. On the other hand, SimpleSAMLphp is detailed as "Application written in native PHP that deals with authentication". It is an award-winning application written in native PHP that deals with authentication. It supports some other identity protocols and frameworks, such as Shibboleth 1.3, A-Select, CAS, OpenID, WS-Federation or OAuth, and is easily extendable, so you can develop your own modules if you like.

OAuth2 and SimpleSAMLphp can be categorized as "User Management and Authentication" tools.

SimpleSAMLphp is an open source tool with 687 GitHub stars and 486 GitHub forks. Here's a link to SimpleSAMLphp's open source repository on GitHub.