I am working on building a platform in my company that will provide a single sign on to all of the internal products to the customer. To do that we need to build an Authorisation server to comply with the OIDC protocol. Earlier we had built the Auth server using the Spring Security OAuth project but since in Spring Security 5.x it is no longer supported we are planning to get over with it as well. Below are the 2 options that I was considering to replace the Spring Auth Server. 1. Keycloak 2. Okta 3. Auth0 Please advise which one to use.
It isn't clear if beside the AuthZ requirement you had others, but given the scenario you described my suggestion would for you to go with Keycloak. First of all because you have already an onpremise IdP and with Keycloak you could maintain that setup (if privacy is a concern). Another important point is configuration and customization: I would assume with Spring OAuth you might have had some custom logic around authentication, this can be easily reconfigured in Keycloak by leveraging SPI (https://www.keycloak.org/docs/latest/server_development/index.html#_auth_spi). Finally AuthZ as a functionality is well developed, based on standard protocols and extensible on Keycloak (https://www.keycloak.org/docs/latest/authorization_services/)
