code: public static boolean verifySignature(EnumMap<FacebookParam, CharSequence> params, String secret) {
      if (null == params || params.isEmpty() )
        return false;
      CharSequence sigParam = params.remove(FacebookParam.SIGNATURE);
      return (null == sigParam) ? false : verifySignature(params, secret, sigParam.toString()); 
    }
docs: Verifies that a signature received matches the expected value.
  Removes FacebookParam.SIGNATURE from params if present.
  @param params a map of parameters and their values, such as one
  obtained from extractFacebookParams; expected to the expected signature
  as the FacebookParam.SIGNATURE parameter
  @param secret
  @return a boolean indicating whether the calculated signature matched the
  expected signature