Add authenticate() method.

Author: gk-brown

README.md

@@ -240,6 +240,15 @@ The connection is opened via a data source identified by `getDataSourceName()`,
 
 Auto-commit is disabled so an entire request will be processed within a single transaction. If the request completes successfully, the transaction is committed. Otherwise, it is rolled back.
 
+### Authentication
+Services that require authentication can override the following method, which returns `true` by default:
+
+```java
+protected boolean authenticate(HttpServletRequest request, HttpServletResponse response) { ... }
+```
+
+If this method returns `false`, the requested operation will not be performed.
+
 ### Request and Repsonse Properties
 The following methods provide access to the request and response objects associated with the current invocation:
 

kilo-server/src/main/java/org/httprpc/kilo/WebService.java

@@ -845,7 +845,11 @@ protected void service(HttpServletRequest request, HttpServletResponse response)
             setConnection(connection);
 
             try {
-                invoke(request, response);
+                if (authenticate(request, response)) {
+                    invoke(request, response);
+                }
+
+                response.flushBuffer();
 
                 if (connection != null) {
                     if (response.getStatus() / 100 == 2) {
@@ -911,6 +915,22 @@ protected String getDataSourceName() {
         return null;
     }
 
+    /**
+     * Authenticates a service request.
+     *
+     * @param request
+     * The HTTP servlet request.
+     *
+     * @param response
+     * The HTTP servlet response.
+     *
+     * @return
+     * {@code true} if the request was authenticated; {@code false}, otherwise.
+     */
+    protected boolean authenticate(HttpServletRequest request, HttpServletResponse response) {
+        return true;
+    }
+
     /**
      * Invokes a service method.
      *