public function getIamPolicy($resource, array $optionalArgs = [])
    {
        $request = new GetIamPolicyRequest();
        $request->setResource($resource);

        $requestParams = new RequestParamsHeaderDescriptor([
          'resource' => $request->getResource(),
        ]);
        $optionalArgs['headers'] = isset($optionalArgs['headers'])
            ? array_merge($requestParams->getHeader(), $optionalArgs['headers'])
            : $requestParams->getHeader();

        return $this->startCall(
            'GetIamPolicy',
            Policy::class,
            $optionalArgs,
            $request,
            Call::UNARY_CALL,
            'google.iam.v1.IAMPolicy'
        )->wait();
    }