code: func (w *keystoreWallet) SignTextWithPassphrase(account accounts.Account, passphrase string, text []byte) ([]byte, error) {
  	// Make sure the requested account is contained within
  	if !w.Contains(account) {
  		return nil, accounts.ErrUnknownAccount
  	}
  	// Account seems valid, request the keystore to sign
  	return w.keystore.SignHashWithPassphrase(account, passphrase, accounts.TextHash(text))
  }
docs: // SignTextWithPassphrase implements accounts.Wallet, attempting to sign the
  // given hash with the given account using passphrase as extra authentication.