code: func AddToPropagateCtx(ctx context.Context, key string, val interface{}) context.Context {
  	propagate := ToMap(ctx)
  	propagate[key] = val
  	return context.WithValue(ctx, constants.PropagateCtxKey, propagate)
  }
docs: // AddToPropagateCtx adds a key and value that will be propagated through RPC calls