updating audience from baseUrl to clientId (GoogleCloudPlatform#700)

Author: jabubake

iap/README.md

@@ -26,6 +26,7 @@ It will be used to test both the authorization of an incoming request to an IAP
 - [Enable](https://cloud.google.com/iap/docs/app-engine-quickstart) Identity-Aware Proxy on the App Engine app.
 - Add the service account email to the Identity-Aware Proxy access list for the project.
 - Set the environment variable `IAP_PROTECTED_URL` to point to `https://your-project-id.appspot.com`
+- Set the environment variable `IAP_CLIENT_ID` to point to the [OAuth 2.0 Client ID](https://console.cloud.google.com/apis/credentials) of your IAP protected App Engine Application.
 - Run the integration test:
 ```
     mvn -Dtest=com.example.iap.BuildAndVerifyIapRequestIT verify

iap/src/main/java/com/example/iap/BuildIapRequest.java

@@ -50,13 +50,6 @@ public class BuildIapRequest {
 
   private BuildIapRequest() {}
 
-  private static String getBaseUrl(URL url) throws Exception {
-    String urlFilePath = url.getFile();
-    int pathDelim = urlFilePath.lastIndexOf('/');
-    String path = (pathDelim > 0) ? urlFilePath.substring(0, pathDelim) : "";
-    return (url.getProtocol() + "://" + url.getHost() + path).trim();
-  }
-
   private static ServiceAccountCredentials getCredentials() throws Exception {
     GoogleCredentials credentials =
         GoogleCredentials.getApplicationDefault().createScoped(Collections.singleton(IAM_SCOPE));
@@ -67,7 +60,7 @@ private static ServiceAccountCredentials getCredentials() throws Exception {
     return (ServiceAccountCredentials) credentials;
   }
 
-  private static String getSignedJWToken(ServiceAccountCredentials credentials, String baseUrl)
+  private static String getSignedJWToken(ServiceAccountCredentials credentials, String iapClientId)
       throws IOException {
     Instant now = Instant.now(clock);
     long expirationTime = now.getEpochSecond() + EXPIRATION_TIME_IN_SECONDS;
@@ -80,7 +73,7 @@ private static String getSignedJWToken(ServiceAccountCredentials credentials, St
         .setSubject(credentials.getClientEmail())
         .setIssuedAt(Date.from(now))
         .setExpiration(Date.from(Instant.ofEpochSecond(expirationTime)))
-        .claim("target_audience", baseUrl)
+        .claim("target_audience", iapClientId)
         .signWith(SignatureAlgorithm.RS256, credentials.getPrivateKey())
         .compact();
   }
@@ -105,16 +98,22 @@ private static String getGoogleIdToken(String jwt) throws Exception {
     return idToken;
   }
 
-  public static HttpRequest buildIAPRequest(HttpRequest request) throws Exception {
+  /**
+   * Clone request and add an IAP Bearer Authorization header with signed JWT token.
+   * @param request Request to add authorization header
+   * @param iapClientId OAuth 2.0 client ID for IAP protected resource
+   * @return Clone of request with Bearer style authorization header with signed jwt token.
+   * @throws Exception
+   */
+  public static HttpRequest buildIAPRequest(HttpRequest request, String iapClientId) throws Exception {
     // get service account credentials
     ServiceAccountCredentials credentials = getCredentials();
     // get the base url of the request URL
-    String baseUrl = getBaseUrl(request.getUrl().toURL());
-    String jwt = getSignedJWToken(credentials, baseUrl);
+    String jwt = getSignedJWToken(credentials, iapClientId);
     if (jwt == null) {
       throw new Exception(
           "Unable to create a signed jwt token for : "
-              + baseUrl
+              + iapClientId
               + "with issuer : "
               + credentials.getClientEmail());
     }

iap/src/test/java/com/example/iap/BuildAndVerifyIapRequestIT.java

@@ -34,12 +34,14 @@
 public class BuildAndVerifyIapRequestIT {
 
   private String iapProtectedUrl = System.getenv("IAP_PROTECTED_URL");
+  private String iapClientId = System.getenv("IAP_CLIENT_ID");
   private HttpTransport httpTransport = new NetHttpTransport();
   private VerifyIapRequestHeader verifyIapRequestHeader = new VerifyIapRequestHeader();
 
   @Before
   public void setUp() {
     assertNotNull(iapProtectedUrl);
+    assertNotNull(iapClientId);
   }
 
   // Access an IAP protected url without signed jwt authorization header
@@ -59,7 +61,7 @@ public void accessIapProtectedResourceFailsWithoutJwtHeader() throws Exception {
   public void testGenerateAndVerifyIapRequestIsSuccessful() throws Exception {
     HttpRequest request =
         httpTransport.createRequestFactory().buildGetRequest(new GenericUrl(iapProtectedUrl));
-    HttpRequest iapRequest = buildIAPRequest(request);
+    HttpRequest iapRequest = buildIAPRequest(request, iapClientId);
     HttpResponse response = iapRequest.execute();
     assertEquals(response.getStatusCode(), HttpStatus.SC_OK);
     String headerWithtoken = response.parseAsString();