How to get Cognito SAML integration to sign AuthnRequest?

Hi,

Cognito doesn't support AuthnRequest signing at this time. The assertion consumer endpoint for Cognito user pool doesn't change for the user pool (unless you change the user pool domain), so is the SP entity Id. These values must be per-configured in the IdP and usually if the AuthnRequest has any different values the request will be rejected by the IdP.

More details on federating to SAML IdP from Cognito user pool.