How to use the google-gax.GoogleAuth function in google-gax

BigtableTableAdminClient: Object.assign(
        {
          servicePath: customEndpoint
            ? customEndpointBaseUrl
            : defaultAdminBaseUrl,
          port: customEndpoint ? parseInt(customEndpointPort, 10) : 443,
          sslCreds: customEndpoint
            ? grpc.credentials.createInsecure()
            : undefined,
        },
        options
      ),
    };

    this.api = {};
    this.auth = new GoogleAuth(options);
    this.projectId = options.projectId || '{{projectId}}';
    this.appProfileId = options.appProfileId;
    this.projectName = `projects/${this.projectId}`;
    this.shouldReplaceProjectIdToken = this.projectId === '{{projectId}}';
  }