Impersonated credentials verify token sample

ImpersonatedCredentials.java

  @Override
  public String getIdToken(String targetAudience, boolean includeEmail) {
    String token;
    try {
      token = getOIDCToken(targetAudience, includeEmail);
    } catch (IOException ex) {
      throw new IdTokenProviderException("Failed to get IdToken ", ex);
    }
    return token;
  }

  private String getOIDCToken(String targetAudience, boolean includeEmail) throws IOException{
    String signBlobUrl = String.format(IAM_ID_TOKEN_ENDPOINT, getAccount());
    GenericUrl genericUrl = new GenericUrl(signBlobUrl);

    GenericData signRequest = new GenericData();
    signRequest.set("delegates", this.delegates);
    signRequest.set("audience", targetAudience);
    signRequest.set("includeEmail", includeEmail);    
    JsonHttpContent signContent = new JsonHttpContent(OAuth2Utils.JSON_FACTORY, signRequest);
    HttpTransport httpTransport = this.transportFactory.create();
    HttpCredentialsAdapter adapter = new HttpCredentialsAdapter(sourceCredentials);
    HttpRequestFactory requestFactory = httpTransport.createRequestFactory();

    HttpRequest request = requestFactory.buildPostRequest(genericUrl, signContent);
    Map<String, List<String>> headers = getRequestMetadata();
    HttpHeaders requestHeaders = request.getHeaders();
    for (Map.Entry<String, List<String>> entry : headers.entrySet()) {
      requestHeaders.put(entry.getKey(), entry.getValue());
    }
    JsonObjectParser parser = new JsonObjectParser(OAuth2Utils.JSON_FACTORY);
    adapter.initialize(request);
    request.setParser(parser);
    request.setThrowExceptionOnExecuteError(false);

    HttpResponse response = request.execute();
    int statusCode = response.getStatusCode();
    if (statusCode >= 400 && statusCode < HttpStatusCodes.STATUS_CODE_SERVER_ERROR) {
      GenericData responseError = response.parseAs(GenericData.class);
      Map<String, Object> error = OAuth2Utils.validateMap(responseError, "error", PARSE_ERROR_MESSAGE);
      String errorMessage = OAuth2Utils.validateString(error, "message", PARSE_ERROR_MESSAGE);
      throw new IOException(String.format("Error code %s trying to getIDToken: %s",
          statusCode, errorMessage));
    }
    if (statusCode != HttpStatusCodes.STATUS_CODE_OK) {
      throw new IOException(String.format("Unexpected Error code %s trying to getIDToken: %s", statusCode,
          response.parseAsString()));
    }
    InputStream content = response.getContent();
    if (content == null) {
      // Throw explicitly here on empty content to avoid NullPointerException from parseAs call.
      // Mock transports will have success code with empty content by default.
      throw new IOException("Empty content from idToken request.");
    }

    GenericData responseData = response.parseAs(GenericData.class);
    return OAuth2Utils.validateString(responseData, "token", PARSE_ERROR_SIGNATURE);
  }