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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ssh_init_sec_context( self, target, desired_mech=None, username=None, recv_token=None ):
 """ Initialize a SSPI context. :param str username: The name of the user who attempts to login :param str target: The FQDN of the target to connect to :param str desired_mech: The negotiated SSPI mechanism ("pseudo negotiated" mechanism, because we support just the krb5 mechanism :-)) :param recv_token: The SSPI token received from the Server :raises: `.SSHException` -- Is raised if the desired mechanism of the client is not supported :return: A ``String`` if the SSPI has returned a token or ``None`` if no token was returned """

        from pyasn1.codec.der import decoder

        self._username = username
        self._gss_host = target
        error = 0
        targ_name = "host/" + self._gss_host
        if desired_mech is not None:
            mech, __ = decoder.decode(desired_mech)
            if mech.__str__() != self._krb5_mech:
                raise SSHException("Unsupported mechanism OID.")
        try:
            if recv_token is None:
                self._gss_ctxt = sspi.ClientAuth(
                    "Kerberos", scflags=self._gss_flags, targetspn=targ_name
                )
            error, token = self._gss_ctxt.authorize(recv_token)
            token = token[0].Buffer
        except pywintypes.error as e:
            e.strerror += ", Target: {}".format(e, self._gss_host)
            raise

        if error == 0:
            """
            if the status is GSS_COMPLETE (error = 0) the context is fully
            established an we can set _gss_ctxt_status to True.
            """
            self._gss_ctxt_status = True
            token = None
            """
            You won't get another token if the context is fully established,
            so i set token to None instead of ""
            """
        return token