Create a PHP authentication system

I need a skeletal authentication system for a PHP app, the app already exists but I need the authentication system created. The authentication should work like Zendesk's authentication in that users should be able to exist locally but also authenticate against a SAML Identity provider (such as Okta or OneLogin) or popular enterprise services such as Google. Zendesk requires at least 1 local account for managing the system and the rest of the users are created either locally, authenticate using SAML connector to an identity provider such as OneLogin or against a service such as Google (oAuth is acceptable). To summarise: - I need scripts that I can POST data to using PHP that either authenticate/create a user or return a registration/login error. - The app administrator should be able to connect to app to a SAML identity provider - The authentication system should work exactly the same as Zendesk's system at [login to view URL] The traditional part of the authentication system must utilise bcrypt, blowfish and salting for security.