code: public static boolean verifySignature(EnumMap<FacebookParam, CharSequence> params, String secret,
                                          String expected) {
      assert !(null == secret || "".equals(secret));
      if (null == params || params.isEmpty() )
        return false;
      if (null == expected || "".equals(expected)) {
        return false;
      }
      params.remove(FacebookParam.SIGNATURE);
      List<String> sigParams = convertFacebookParams(params.entrySet());
      return verifySignature(sigParams, secret, expected);
    }
docs: Verifies that a signature received matches the expected value.
  @param params a map of parameters and their values, such as one
  obtained from extractFacebookParams
  @return a boolean indicating whether the calculated signature matched the
  expected signature