184.108.40.206.2 SAML-P Extensions for Preauthentication
The server MUST validate that the request meets the conditions to issue pre-authentication (section 220.127.116.11) for the web application in [Server State].RelyingPartyTrusts with identifiers containing a string value that matches the <Issuer> element value ([SAMLCore2] section 2.2.5) in the <AuthnRequest> element ([SAMLCore2].
Upon successful authentication ([SAMLCore2] section 18.104.22.168) the server MUST do the following before sending the response to the response URL:
Transform the response URL based on the values of [Relying Party Trust].proxyEndpointMappings for the web application by replacing the response URL string portion that matches the Key value (internal URL mapping value) with the value of Value (external URL mapping value). If there is no match the response URL MUST not be changed.
If the request is an IdP initiated request the server MUST perform authentication of the request based on the server's authentication policy for [Server State].ProxyRelyingPartyTrust. If authentication fails the server MUST respond according to [SAMLCore2] defined behavior for failed authentication.
If authentication succeeds the server MUST include in the response URL a query string parameter with name "authToken" with a value of a base64url encoded ([RFC4648] section 5) proxy token (section 22.214.171.124).
The server MUST send the response to the response URL.