typedef void (*SilcGetAuthMeth)(SilcAuthMethod auth_meth,
                                    const void *auth, SilcUInt32 auth_len,
                                    void *context);

    Authentication data resolving callback. This is called by the
    application to return the resolved authentication data. The client
    library has called the get_auth_method client operation and given
    this function pointer as argument. The `auth_meth' is the selected
    authentication method. The `auth_data' and the `auth_data_len'
    are the resolved authentication data. The `context' is the libary's
    context sent to the get_auth_method client operation.

    If the `auth_method' is SILC_AUTH_PASSWORD then `auth' and `auth_len'
    is the passphrase and its length.  If it is SILC_AUTH_PUBLIC_KEY the
    `auth' must be NULL.  The library will use the private key given as
    argument to silc_client_connect_to_server, silc_client_connect_to_client
    or silc_client_key_exchange.  If it is SILC_AUTH_NONE, both `auth' and
    `auth_len' are ignored.