Calculates a MIC (message integrity checksum) for the given
message, and returns it together with the message, which is
optionally encrypted. The returned value can be verified and (if
applicable) decrypted by the receiver using unwrap or some
other GSS_Unwrap wrapper.
This wraps GSS_Wrap according to RFC 2743 section 2.3.3.
This function requires that the context is established, or that
the early per-message protection service is available (c.f.
GSSAPI.PROT_READY_FLAG . If not, a
GSSAPI.MissingServicesError is thrown (but the context is not
closed).