title: Setting grpc metadata in http request
body: <p>I am trying to create REST endpoints for an existing gRPC service using grpc-gateway. The gRPC service makes use of "metadata" passed in grpc calls to authenticate.
  How do I set the metadata in my REST calls?</p>
  
  <p>I have tried passing metadata key value pairs in the headers. But it did not set the metadata in context.</p>