GUACAMOLE-220: Manually recurse through the group membership graph if the database engine does not support recursive queries.

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-postgresql/src/main/java/org/apache/guacamole/auth/postgresql/PostgreSQLEnvironment.java

@@ -242,5 +242,10 @@ public class PostgreSQLEnvironment extends JDBCEnvironment {
     public String getPostgreSQLPassword() throws GuacamoleException {
         return getRequiredProperty(PostgreSQLGuacamoleProperties.POSTGRESQL_PASSWORD);
     }
+
+    @Override
+    public boolean isRecursiveQuerySupported() {
+        return true; // All versions of PostgreSQL support recursive queries through CTEs
+    }
     
 }