Class HMACSign

include/jwt/algorithm.hpp:333–398

 */
template <typename Hasher>
struct HMACSign
{
  /// The type of Hashing algorithm
  using hasher_type = Hasher;

  /**
   * Signs the input using the HMAC algorithm using the
   * provided key.
   *
   * Arguments:
   *  @key : The secret/key to use for the signing.
   *         Cannot be empty string.
   *  @data : The data to be signed.
   *
   *  Exceptions:
   *    Any allocation failure will result in jwt::MemoryAllocationException
   *    being thrown.
   */
  static sign_result_t sign(const jwt::string_view key, const jwt::string_view data)
  {
    std::string sign;
    sign.resize(EVP_MAX_MD_SIZE);
    std::error_code ec{};

    uint32_t len = 0;

    unsigned char* res = HMAC(Hasher{}(),
                              key.data(),
                              static_cast<int>(key.length()),
                              reinterpret_cast<const unsigned char*>(data.data()),
                              data.length(),
                              reinterpret_cast<unsigned char*>(&sign[0]),
                              &len);
    if (!res) {
      ec = AlgorithmErrc::SigningErr;
    }

    sign.resize(len);
    return { std::move(sign), ec };
  }

  /**
   * Verifies the JWT string against the signature using
   * the provided key.
   *
   * Arguments:
   *  @key : The secret/key to use for the signing.
   *         Cannot be empty string.
   *  @head : The part of JWT encoded string representing header
   *          and the payload claims.
   *  @sign : The signature part of the JWT encoded string.
   *
   *  Returns:
   *    verify_result_t
   *    verify_result_t::first set to true if verification succeeds.
   *    false otherwise.
   *    verify_result_t::second set to relevant error if verification fails.
   *