Performing Mutual Authentication Between Peers in GSS-API

A user who transfers files to an ftp site typically does not need proof of the site's identity. On the other hand, a user who is required to provide a credit card number to an application would want definite proof of the receiver's identity. In such a case, mutual authentication is required. Both the context initiator and the acceptor must prove their identities.

A context initiator can request mutual authentication by setting the gss_init_sec_context() req_flags argument to the value GSS_C_MUTUAL_FLAG. If mutual authentication has been authorized, the function indicates authorization by setting the ret_flags argument to this value. If mutual authentication is requested but not available, the initiating application is responsible for responding accordingly. GSS-API does not automatically terminate a context when mutual authentication is requested but unavailable. Also, some mechanisms always perform mutual authentication even without a specific request.