Final answer:
IDP-initiated sign on flow begins with the user logging into the IDP's portal and then accessing various services, whereas SP-initiated sign on flow starts when a user tries to access a service and is then redirected to the IDP for authentication.
Step-by-step explanation:
Distinguishing Identity Provider (IDP) Versus Service Provider (SP) Initiated Sign On Flows
The difference between Identity Provider (IDP) and Service Provider (SP) initiated sign on flows lies in the initiation point of the login process in a Single Sign-On (SSO) system. In an IDP-initiated sign on, the user first logs into their IDP's portal and then selects the SP they wish to access, which allows for authentication without the need to provide credentials again. Conversely, in an SP-initiated sign on, the user attempts to access a service or application, and if not authenticated, is redirected to their IDP for authentication. After providing their credentials to the IDP, the user is redirected back to the SP with an authentication token. Each flow offers different implications for user convenience and system security.
An example of IDP-initiated sign on might be a corporate portal where employees select services they are authorized to use after logging in. As for an example of SP-initiated sign on, consider a user trying to access a cloud application such as a project management system, being redirected to authenticate, and then gaining access to the system.