grpc/ttnctx/context.go
func IDFromMetadata(md metadata.MD) (string, error) {
	id, ok := md["id"]
	if !ok || len(id) == 0 {
		return "", ErrNoID
	}
	return id[0], nil
}
func IDFromMetadata(md metadata.MD) (string, error) {
	id, ok := md["id"]
	if !ok || len(id) == 0 {
		return "", ErrNoID
	}
	return id[0], nil
}
// IDFromMetadata gets the key from the metadata or returns ErrNoID