docs(samples): modified comments in the samples and minor refactor

samples/snippets/src/main/java/AuthenticateImplicitWithAdc.java

@@ -16,19 +16,22 @@
 
 // [START auth_cloud_implicit_adc]
 
-import com.google.cloud.compute.v1.Instance;
-import com.google.cloud.compute.v1.InstancesClient;
+import com.google.api.gax.paging.Page;
+import com.google.cloud.storage.Bucket;
+import com.google.cloud.storage.Storage;
+import com.google.cloud.storage.StorageOptions;
 import java.io.IOException;
 
 public class AuthenticateImplicitWithAdc {
 
   public static void main(String[] args) throws IOException {
     // TODO(Developer):
     //  1. Before running this sample,
-    //  set up ADC as described in https://cloud.google.com/docs/authentication/external/set-up-adc
+    //  set up Application Default Credentials as described in
+    //  https://cloud.google.com/docs/authentication/external/set-up-adc
     //  2. Replace the project variable below.
-    //  3. Make sure that the user account or service account that you are using
-    //  has the required permissions. For this sample, you must have "compute.instances.list".
+    //  3. Make sure you have the necessary permission to list storage buckets
+    //  "storage.buckets.list"
     String projectId = "your-google-cloud-project-id";
     authenticateImplicitWithAdc(projectId);
   }
@@ -37,24 +40,20 @@ public static void main(String[] args) throws IOException {
   // credentials to use.
   public static void authenticateImplicitWithAdc(String project) throws IOException {
 
-    String zone = "us-central1-a";
-    // This snippet demonstrates how to list instances.
     // *NOTE*: Replace the client created below with the client required for your application.
     // Note that the credentials are not specified when constructing the client.
     // Hence, the client library will look for credentials using ADC.
     //
     // Initialize client that will be used to send requests. This client only needs to be created
-    // once, and can be reused for multiple requests. After completing all of your requests, call
-    // the `instancesClient.close()` method on the client to safely
-    // clean up any remaining background resources.
-    try (InstancesClient instancesClient = InstancesClient.create()) {
-      // Set the project and zone to retrieve instances present in the zone.
-      System.out.printf("Listing instances from %s in %s:", project, zone);
-      for (Instance zoneInstance : instancesClient.list(project, zone).iterateAll()) {
-        System.out.println(zoneInstance.getName());
-      }
-      System.out.println("####### Listing instances complete #######");
+    // once, and can be reused for multiple requests.
+    Storage storage = StorageOptions.newBuilder().setProjectId(project).build().getService();
+
+    System.out.println("Buckets:");
+    Page<Bucket> buckets = storage.list();
+    for (Bucket bucket : buckets.iterateAll()) {
+      System.out.println(bucket.toString());
     }
+    System.out.println("Listed all storage buckets.");
   }
 }
 // [END auth_cloud_implicit_adc]

samples/snippets/src/main/java/IdTokenFromImpersonatedCredentials.java

@@ -31,14 +31,13 @@ public static void main(String[] args) throws IOException {
 
     // Provide the scopes that you might need to request to access Google APIs,
     // depending on the level of access you need.
-    // The best practice is to use the cloud-wide scope and use IAM to narrow the permissions.
-    // https://cloud.google.com/docs/authentication#authorization_for_services
+    // This example uses the cloud-wide scope and uses IAM to narrow the permissions.
+    // https://cloud.google.com/docs/authentication/external/authorization-gcp
     // For more information, see: https://developers.google.com/identity/protocols/oauth2/scopes
     String scope = "https://www.googleapis.com/auth/cloud-platform";
 
-    // The service name for which the id token is requested. Service name refers to the
-    // logical identifier of an API service, such as "pubsub.googleapis.com".
-    String targetAudience = "iap.googleapis.com";
+    // The service name for which the id token is requested.
+    String targetAudience = "https://example.com";
 
     // The name of the privilege-bearing service account for whom the credential is created.
     String impersonatedServiceAccount = "name@project.service.gserviceaccount.com";
@@ -78,8 +77,8 @@ public static void getIdTokenUsingOAuth2(
             .build();
 
     // Get the ID token.
-    // Once you've obtained the ID token, use it to make an authenticated call
-    // to the target audience.
+    // Once you've obtained the ID token, you can use it to make an authenticated call to the
+    // target audience.
     String idToken = idTokenCredentials.refreshAccessToken().getTokenValue();
     System.out.println("Generated ID token.");
   }

samples/snippets/src/main/java/IdTokenFromMetadataServer.java

@@ -30,14 +30,13 @@ public static void main(String[] args) throws IOException, GeneralSecurityExcept
     // TODO(Developer): Replace the below variables before running the code.
 
     // The url or target audience to obtain the ID token for.
-    String url = "http://www.abc.com";
+    String url = "https://example.com";
 
     getIdTokenFromMetadataServer(url);
   }
 
-  // Use the Google Cloud metadata server in the Cloud Run (or AppEngine or Kubernetes etc.,)
-  // environment to create an identity token and add it to the HTTP request as part of an
-  // Authorization header.
+  // Use the Google Cloud metadata server to create an identity token and add it to the
+  // HTTP request as part of an Authorization header.
   public static void getIdTokenFromMetadataServer(String url) throws IOException {
     // Construct the GoogleCredentials object which obtains the default configuration from your
     // working environment.
@@ -52,8 +51,8 @@ public static void getIdTokenFromMetadataServer(String url) throws IOException {
             .build();
 
     // Get the ID token.
-    // Once you've obtained the ID token, use it to make an authenticated call
-    // to the target audience.
+    // Once you've obtained the ID token, you can use it to make an authenticated call to the
+    // target audience.
     String idToken = idTokenCredentials.refreshAccessToken().getTokenValue();
     System.out.println("Generated ID token.");
   }

samples/snippets/src/main/java/IdTokenFromServiceAccount.java

@@ -44,7 +44,7 @@ public static void main(String[] args)
     String jsonCredentialPath = "path-to-json-credential-file";
 
     // The url or target audience to obtain the ID token for.
-    String targetAudience = "http://www.abc.com";
+    String targetAudience = "https://example.com";
 
     getIdTokenFromServiceAccount(jsonCredentialPath, targetAudience);
   }

samples/snippets/src/main/java/VerifyGoogleIdToken.java

@@ -26,9 +26,8 @@ public static void main(String[] args) {
     // The Google ID token to verify.
     String idToken = "id-token";
 
-    // The service name for which the id token is requested. Service name refers to the
-    // logical identifier of an API service, such as "pubsub.googleapis.com".
-    String targetAudience = "pubsub.googleapis.com";
+    // The service name for which the id token was requested.
+    String targetAudience = "https://example.com";
 
     // To verify id tokens, get the Json Web Key endpoint (jwk).
     // OpenID Connect allows the use of a "Discovery document," a JSON document found at a

samples/snippets/src/test/java/SnippetsIT.java

@@ -95,16 +95,16 @@ private static String getIdTokenFromServiceAccount(
 
   @Test
   public void testIdTokenFromServiceAccount() throws IOException {
-    IdTokenFromServiceAccount.getIdTokenFromServiceAccount(CREDENTIALS, "iap.googleapis.com");
+    IdTokenFromServiceAccount.getIdTokenFromServiceAccount(CREDENTIALS, "https://example.com");
     assertThat(stdOut.toString()).contains("Generated ID token.");
   }
 
   @Test
   public void testVerifyGoogleIdToken() throws IOException {
-    String idToken = getIdTokenFromServiceAccount(CREDENTIALS, "iap.googleapis.com");
+    String idToken = getIdTokenFromServiceAccount(CREDENTIALS, "https://example.com");
 
     VerifyGoogleIdToken.verifyGoogleIdToken(
-        idToken, "iap.googleapis.com", "https://www.googleapis.com/oauth2/v3/certs");
+        idToken, "https://example.com", "https://www.googleapis.com/oauth2/v3/certs");
   }
 
   @Test