Conventionally, "authn" means authentication, "authz" means authorization, and plain old "auth" doesn't mean anything in particular.
I don't think it makes sense to blame SAML for the awkwardness of using the passive browser sign-in scenario for something for which it was not designed. There are other profiles and other protocols available from any competent security token service.
Also bear in mind there is a tremendous amount of confusion around the SAML terminology, which can mean the token format, or the protocol for exchanging authentication request messages, which are entirely separate things.
Conventionally, "authn" means authentication, "authz" means authorization, and plain old "auth" doesn't mean anything in particular.
I don't think it makes sense to blame SAML for the awkwardness of using the passive browser sign-in scenario for something for which it was not designed. There are other profiles and other protocols available from any competent security token service.
Also bear in mind there is a tremendous amount of confusion around the SAML terminology, which can mean the token format, or the protocol for exchanging authentication request messages, which are entirely separate things.