Unfortunately, no; the auth.backend
configuration as written only supports being configured for the exact strings of the 4 backend types; there doesn't seem to be any mechanism for fallback to another method.
if (!buffer_is_empty(s->auth_backend_conf)) {
if (buffer_is_equal_string(s->auth_backend_conf, CONST_STR_LEN("htpasswd"))) {
s->auth_backend = AUTH_BACKEND_HTPASSWD;
} else if (buffer_is_equal_string(s->auth_backend_conf, CONST_STR_LEN("htdigest"))) {
s->auth_backend = AUTH_BACKEND_HTDIGEST;
} else if (buffer_is_equal_string(s->auth_backend_conf, CONST_STR_LEN("plain"))) {
s->auth_backend = AUTH_BACKEND_PLAIN;
} else if (buffer_is_equal_string(s->auth_backend_conf, CONST_STR_LEN("ldap"))) {
s->auth_backend = AUTH_BACKEND_LDAP;
} else {
log_error_write(srv, __FILE__, __LINE__, "sb", "auth.backend not supported:", s->auth_backend_conf);
return HANDLER_ERROR;
}
}