No, SAML and HTTP Passthrough are different. SAML makes request in XML format to IDP (Identity Provider) and receives response in XML with specific claims that application is setup for. Reason why many organizations are moving toward SAML SSO or similar services is because they may have several different user directories that they want to combine but yet keep them separated, thus you can have 3 different active directories, for vendors, employees, guests, etc. IDPs are there to combine them all in one and use them for your applications. Another great feature is that you don't have to open up your firewall and manage all AD connections through LDAP, IDPs are built to be web based and have many security features in place where LDAP is just a protocol and user have to build security features in their applications.