VerifyClientCallbackAsync is an asynchronous callback used to inspect the
incoming message. The return value (boolean) of the function determines
whether or not to accept the handshake.
VerifyClientCallbackSync is a synchronous callback used to inspect the
incoming message. The return value (boolean) of the function determines
whether or not to accept the handshake.
CertMeta represents the accepted types for certificate & key data.