GUACAMOLE-524: Implements Attributes and provides getAttributes and setAttributes default methods

guacamole-ext/src/main/java/org/apache/guacamole/net/auth/AbstractAuthenticatedUser.java

@@ -20,6 +20,7 @@
 package org.apache.guacamole.net.auth;
 
 import java.util.Collections;
+import java.util.Map;
 import java.util.Set;
 
 /**
@@ -41,4 +42,12 @@ public abstract class AbstractAuthenticatedUser extends AbstractIdentifiable
         // Nothing to invalidate
     }
 
+    public Map<String, String> getAttributes() {
+        return Collections.<String, String>emptyMap();
+    }
+
+    public void setAttributes(Map<String, String> attributes) {
+        //do nothing
+    }
+
 }