code: func (l *State) checkToken(id types.CheckID) string {
  	var token string
  	c := l.checks[id]
  	if c != nil {
  		token = c.Token
  	}
  	if token == "" {
  		token = l.tokens.UserToken()
  	}
  	return token
  }
docs: // checkToken returns an ACL token associated with a check.
  // This method is not synchronized and the lock must already be held.