code: func GetUserMetadata(ctx context.Context) (*UserMetadata, bool) {
  	userMD := ctx.Value(userMDKey{})
  
  	switch md := userMD.(type) {
  	case *UserMetadata:
  		return md, true
  	default:
  		return nil, false
  	}
  }
docs: // GetUserMetadata can be used to extract user metadata stored in a context.