code: func (k *Kontrol) Verify(pub string) error {
  	switch err := k.keyPair.IsValid(pub); err {
  	case nil, ErrKeyDeleted:
  		return nil
  	default:
  		return err
  	}
  }
docs: // Verify is used for token and kiteKey authenticators to verify
  // client's kontrol keys. In order to allow for graceful key
  // updates deleted keys are allowed.
  //
  // If Config.VerifyFunc is nil during Kontrol instantiation with
  // one of New* functions, this is the default verify method
  // used by kontrol kite.