Add App Identity example to assert identity to Google APIs.

appengine/appidentity/pom.xml

@@ -33,13 +33,23 @@ Copyright 2015 Google Inc. All Rights Reserved.
       <artifactId>appengine-api-1.0-sdk</artifactId>
       <version>${appengine.target.version}</version>
     </dependency>
+    <dependency>
+      <groupId>com.google.guava</groupId>
+      <artifactId>guava</artifactId>
+      <version>19.0</version>
+    </dependency>
     <dependency>
       <groupId>javax.servlet</groupId>
       <artifactId>servlet-api</artifactId>
       <version>2.5</version>
       <type>jar</type>
       <scope>provided</scope>
     </dependency>
+    <dependency>
+      <groupId>org.json</groupId>
+      <artifactId>json</artifactId>
+      <version>20151123</version>
+    </dependency>
 
     <!-- Test Dependencies -->
     <dependency>

appengine/appidentity/src/main/java/com/example/appengine/appidentity/UrlShortener.java

@@ -0,0 +1,79 @@
+/**
+ * Copyright 2016 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.example.appengine.appidentity;
+
+import com.google.appengine.api.appidentity.AppIdentityService;
+import com.google.appengine.api.appidentity.AppIdentityServiceFactory;
+import com.google.common.io.CharStreams;
+
+import org.json.JSONObject;
+import org.json.JSONTokener;
+
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
+import java.net.HttpURLConnection;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+
+@SuppressWarnings("serial")
+class UrlShortener {
+  // [START asserting_identity_to_Google_APIs]
+  /**
+   * Returns a shortened URL by calling the Google URL Shortener API.
+   *
+   * <p>Note: Error handling elided for simplicity.
+   */
+  public String createShortUrl(String longUrl) throws Exception {
+    ArrayList<String> scopes = new ArrayList<String>();
+    scopes.add("https://www.googleapis.com/auth/urlshortener");
+    AppIdentityService appIdentity = AppIdentityServiceFactory.getAppIdentityService();
+    AppIdentityService.GetAccessTokenResult accessToken = appIdentity.getAccessToken(scopes);
+    // The token asserts the identity reported by appIdentity.getServiceAccountName()
+    JSONObject request = new JSONObject();
+    request.put("longUrl", longUrl);
+
+    URL url = new URL("https://www.googleapis.com/urlshortener/v1/url?pp=1");
+    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
+    connection.setDoOutput(true);
+    connection.setRequestMethod("POST");
+    connection.addRequestProperty("Content-Type", "application/json");
+    connection.addRequestProperty("Authorization", "Bearer " + accessToken.getAccessToken());
+
+    OutputStreamWriter writer = new OutputStreamWriter(connection.getOutputStream());
+    request.write(writer);
+    writer.close();
+
+    if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
+      // Note: Should check the content-encoding.
+      //       Any JSON parser can be used; this one is used for illustrative purposes.
+      JSONTokener response_tokens = new JSONTokener(connection.getInputStream());
+      JSONObject response = new JSONObject(response_tokens);
+      return (String) response.get("id");
+    } else {
+      try (InputStream s = connection.getErrorStream();
+          InputStreamReader r = new InputStreamReader(s, StandardCharsets.UTF_8)) {
+        throw new RuntimeException(String.format(
+            "got error (%d) response %s from %s",
+            connection.getResponseCode(),
+            CharStreams.toString(r),
+            connection.toString()));
+      }
+    }
+  }
+  // [END asserting_identity_to_Google_APIs]
+}

appengine/appidentity/src/main/java/com/example/appengine/appidentity/UrlShortenerServlet.java

@@ -0,0 +1,73 @@
+/**
+ * Copyright 2016 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.example.appengine.appidentity;
+
+import com.google.appengine.api.users.UserService;
+import com.google.appengine.api.users.UserServiceFactory;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.net.URLDecoder;
+
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+@SuppressWarnings("serial")
+public class UrlShortenerServlet extends HttpServlet {
+  private final UrlShortener shortener;
+
+  public UrlShortenerServlet() {
+    shortener = new UrlShortener();
+  }
+
+  @Override
+  public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
+    PrintWriter w = resp.getWriter();
+    w.println("<!DOCTYPE html>");
+    w.println("<form method='post'>");
+    w.println("<label for='longUrl'>URL:</label>");
+    w.println("<input id='longUrl' name='longUrl' type='text'>");
+    w.println("<input type='submit' value='Shorten'>");
+    w.println("</form>");
+  }
+
+  @Override
+  public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
+    resp.setContentType("text/plain");
+    String longUrl = req.getParameter("longUrl");
+    if (longUrl == null) {
+      resp.sendError(HttpServletResponse.SC_BAD_REQUEST, "missing longUrl parameter");
+      return;
+    }
+
+    String shortUrl;
+    PrintWriter w = resp.getWriter();
+    try {
+      shortUrl = shortener.createShortUrl(longUrl);
+    } catch (Exception e) {
+      resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
+      w.println("error shortening URL: " + longUrl);
+      e.printStackTrace(w);
+      return;
+    }
+
+    w.print("long URL: ");
+    w.println(longUrl);
+    w.print("short URL: ");
+    w.println(shortUrl);
+  }
+}

appengine/appidentity/src/main/webapp/WEB-INF/web.xml

@@ -7,8 +7,16 @@
     <servlet-name>appidentity</servlet-name>
     <servlet-class>com.example.appengine.appidentity.IdentityServlet</servlet-class>
   </servlet>
+  <servlet>
+    <servlet-name>urlshortener</servlet-name>
+    <servlet-class>com.example.appengine.appidentity.UrlShortenerServlet</servlet-class>
+  </servlet>
   <servlet-mapping>
     <servlet-name>appidentity</servlet-name>
     <url-pattern>/</url-pattern>
   </servlet-mapping>
+  <servlet-mapping>
+    <servlet-name>urlshortener</servlet-name>
+    <url-pattern>/shorten</url-pattern>
+  </servlet-mapping>
 </web-app>