Normalize/canonicalize ``self.gss_host`` depending on various factors.

        :param str gss_host:
            The explicitly requested GSS-oriented hostname to connect to (i.e.
            what the host's name is in the Kerberos database.) Defaults to
            ``self.hostname`` (which will be the 'real' target hostname and/or
            host portion of given socket object.)
        :param bool trust_dns:
            Indicates whether or not DNS is trusted; if true, DNS will be used
            to canonicalize the GSS hostname (which again will either be
            ``gss_host`` or the transport's default hostname.)
            (Defaults to True due to backwards compatibility.)
        :param bool gssapi_requested:
            Whether GSSAPI key exchange or authentication was even requested.
            If not, this is a no-op and nothing happens
            (and ``self.gss_host`` is not set.)
            (Defaults to True due to backwards compatibility.)
        :returns: ``None``.

def set_gss_host(self, gss_host, trust_dns=True, gssapi_requested=True):
        """
        Normalize/canonicalize ``self.gss_host`` depending on various factors.

        :param str gss_host:
            The explicitly requested GSS-oriented hostname to connect to (i.e.
            what the host's name is in the Kerberos database.) Defaults to
            ``self.hostname`` (which will be the 'real' target hostname and/or
            host portion of given socket object.)
        :param bool trust_dns:
            Indicates whether or not DNS is trusted; if true, DNS will be used
            to canonicalize the GSS hostname (which again will either be
            ``gss_host`` or the transport's default hostname.)
            (Defaults to True due to backwards compatibility.)
        :param bool gssapi_requested:
            Whether GSSAPI key exchange or authentication was even requested.
            If not, this is a no-op and nothing happens
            (and ``self.gss_host`` is not set.)
            (Defaults to True due to backwards compatibility.)
        :returns: ``None``.
        """
        # No GSSAPI in play == nothing to do
        if not gssapi_requested:
            return
        # Obtain the correct host first - did user request a GSS-specific name
        # to use that is distinct from the actual SSH target hostname?
        if gss_host is None:
            gss_host = self.hostname
        # Finally, canonicalize via DNS if DNS is trusted.
        if trust_dns and gss_host is not None:
            gss_host = socket.getfqdn(gss_host)
        # And set attribute for reference later.
        self.gss_host = gss_host