typedef SilcBool
    (*SilcConnAuthGetAuthData)(SilcConnAuth connauth,
                               SilcConnectionType conn_type,
                               unsigned char **passphrase,
                               SilcUInt32 *passphrase_len,
                               SilcSKR *repository,
                               void *context);

    Authentication callback to retrieve the authentication data from the
    application.  This is responder callback.  If the authentication
    method is passphrase it must be returned to `passphrase' pointer.
    If it is digital signatures the key repository pointer must be
    returned into `repository' pointer, which the library will use to
    find the correct public key to verify the digital signature.  If
    neither `passphrase' or `repository' is set but TRUE is returned,
    authentication is not required.

    If this connection is not configured at all this returns FALSE which
    will result into authentication failure.  Otherwise TRUE must be
    returned.