core/play/src/main/java/play/libs/crypto/DefaultCookieSigner.java
@Override
  public String sign(String message, byte[] key) {
    return signer.sign(message, key);
  }
@Override
  public String sign(String message, byte[] key) {
    return signer.sign(message, key);
  }
Signs the given String using the given key. <br>

@param message The message to sign.
@param key The private key to sign with.
@return A hexadecimal encoded signature.