SilcBuffer silc_auth_payload_encode(SilcAuthMethod method,
                                        const unsigned char *random_data,
                                        SilcUInt16 random_len,
                                        const unsigned char *auth_data,
                                        SilcUInt16 auth_len);

    Encodes authentication payload into buffer and returns it.
    The `random_data' is provided only if doing public key authentication.
    The `auth_data' is the actual authentication data.  If the
    `method' is SILC_AUTH_PASSWORD the passphase in `auth_data' sent as
    argument SHOULD be UTF-8 encoded, if not library will attempt to
    encode it.