When a user logs into a Service Provider (SP), what does the SP do next?

When a user logs into a Service Provider (SP), the next step involves a process known as authentication, which typically requires interaction with an Identity Provider (IdP). The Service Provider, not having the user's authentication credentials, must forward the user's request to the IdP to verify the user's identity. This step is essential because the IdP is responsible for authenticating users and providing the necessary assertions that confirm the user's identity to the SP.

By forwarding the request to the IdP, the SP relies on the IdP's mechanisms to handle user authentication securely. Once this step is completed, the IdP will respond to the SP with either a positive or negative authentication outcome, allowing the SP to grant or deny access based on that result.

In contrast, if the SP were to directly log the user in without this verification, it would bypass critical security measures, potentially exposing the application to unauthorized access. Simply redirecting the user to the cloud or requesting the user's full profile does not align with the fundamental flow of the authentication process involving SPs and IdPs. Therefore, the forwarding of the request to the IdP is a crucial step in maintaining the security and integrity of the authentication process.