GUACAMOLE-393: Add session invalidation hooks to AuthenticatedUser.

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

@@ -29,4 +29,9 @@ public abstract class AbstractAuthenticatedUser extends AbstractIdentifiable
 
     // Prior functionality now resides within AbstractIdentifiable
 
+    @Override
+    public void invalidate() {
+        // Nothing to invalidate
+    }
+
 }

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

@@ -49,4 +49,11 @@ public interface AuthenticatedUser extends Identifiable {
      */
     Credentials getCredentials();
 
+    /**
+     * Invalidates this authenticated user and their associated token such that
+     * they are no longer logged in. This function will be automatically
+     * invoked when the user logs out, or when their session expires.
+     */
+    void invalidate();
+
 }