I am in the process of building an integration between 2 service providers (SP). I have setup my own Identity Provider, KeyCloak.
What I am trying to achieve is as follows: A user signs into SP1 using SSO, they get redirected to our IDP to sign in. They sign in successfully and are redirected back to SP1. Within SP1 a user can access SP2 via a link. I want this user to be automatically signed into SP2 instead of having to re-authN themselves.
I am attempting to implement this solution using KeyCloak as my IDP and SAML as the authentication mechanism. However, I am currently stuck on the following: how does SP2 get informed that a valid and authN'd user is being sent there by SP1? Is there some sort of SAML file that must be shared? How does SP1 go about sharing this information with SP2?