I am looking at a use case where the service provider will need to capture the user id (not password) to identify the target IDP. In this case, the requirement is to send the user id (that is already captured at service provider end) to IDP, so that IDP can pre-populate the user ID while asking for password to end user.
Is there a standard in SAML how this information can be passed from SP to IDP? I am using SP initiated SAML where SAMLRequest and RelayState will be passed from SP to IDP.
Thank you.