code: func (tm *tokenManager) check(addr *net.UDPAddr, tokenString string) bool {
  	key := addr.IP.String()
  	v, ok := tm.Get(key)
  	tk, _ := v.(token)
  
  	if ok {
  		tm.Delete(key)
  	}
  
  	return ok && tokenString == tk.data
  }
docs: // check returns whether the token is valid.