エラー secretOrPrivateKey must be a symmetric key when using HS256

次のエラーにハマった。

secretOrPrivateKey must be a symmetric key when using HS256

nestjsでjwtモジュールを使っているときにでてきた。

    this.jwtService.signAsync(payload, {
        secret: this.configService
          .get('auth.jwtSecret.accessToken')
          .replace(/\\n/g, '\n'),
        expiresIn: 60 * 60,
      }),

エラーの原因。

• アルゴリズムにHS256を指定、もしくは何も指定しない(デフォルトでHS256が選択)
• secretの値に、ssh-keygen -m PEM -t rsaで生成した秘密鍵を指定していた。

すると121行目にひっかかったみたい。

jsonwebtoken

module.exports = function (payload, secretOrPrivateKey, options, callback) {
  if (typeof options === 'function') {
    callback = options;
    options = {};
  } else {
    options = options || {};
  }

  const isObjectPayload = typeof payload === 'object' &&
                        !Buffer.isBuffer(payload);

  const header = Object.assign({
    alg: options.algorithm || 'HS256',
    typ: isObjectPayload ? 'JWT' : undefined,
    kid: options.keyid
  }, options.header);

  function failure(err) {
    if (callback) {
      return callback(err);
    }
    throw err;
  }

  if (!secretOrPrivateKey && options.algorithm !== 'none') {
    return failure(new Error('secretOrPrivateKey must have a value'));
  }

  if (secretOrPrivateKey != null && !(secretOrPrivateKey instanceof KeyObject)) {
    try {
      secretOrPrivateKey = createPrivateKey(secretOrPrivateKey)
    } catch (_) {
      try {
        secretOrPrivateKey = createSecretKey(typeof secretOrPrivateKey === 'string' ? Buffer.from(secretOrPrivateKey) : secretOrPrivateKey)
      } catch (_) {
        return failure(new Error('secretOrPrivateKey is not valid key material'));
      }
    }
  }

  if (header.alg.startsWith('HS') && secretOrPrivateKey.type !== 'secret') {
    return failure(new Error((`secretOrPrivateKey must be a symmetric key when using ${header.alg}`)))
  } else if (/^(?:RS|PS|ES)/.test(header.alg)) {
    if (secretOrPrivateKey.type !== 'private') {
      return failure(new Error((`secretOrPrivateKey must be an asymmetric key when using ${header.alg}`)))
    }
    if (!options.allowInsecureKeySizes &&
      !header.alg.startsWith('ES') &&
      secretOrPrivateKey.asymmetricKeyDetails !== undefined && //KeyObject.asymmetricKeyDetails is supported in Node 15+
      secretOrPrivateKey.asymmetricKeyDetails.modulusLength < 2048) {
      return failure(new Error(`secretOrPrivateKey has a minimum key size of 2048 bits for ${header.alg}`));
    }
  }

  if (typeof payload === 'undefined') {
    return failure(new Error('payload is required'));
  } else if (isObjectPayload) {
    try {
      validatePayload(payload);
    }
    catch (error) {
      return failure(error);
    }
    if (!options.mutatePayload) {
      payload = Object.assign({},payload);
    }
  } else {
    const invalid_options = options_for_objects.filter(function (opt) {
      return typeof options[opt] !== 'undefined';
    });

    if (invalid_options.length > 0) {
      return failure(new Error('invalid ' + invalid_options.join(',') + ' option for ' + (typeof payload ) + ' payload'));
    }
  }

  if (typeof payload.exp !== 'undefined' && typeof options.expiresIn !== 'undefined') {
    return failure(new Error('Bad "options.expiresIn" option the payload already has an "exp" property.'));
  }

  if (typeof payload.nbf !== 'undefined' && typeof options.notBefore !== 'undefined') {
    return failure(new Error('Bad "options.notBefore" option the payload already has an "nbf" property.'));
  }

  try {
    validateOptions(options);
  }
  catch (error) {
    return failure(error);
  }

  if (!options.allowInvalidAsymmetricKeyTypes) {
    try {
      validateAsymmetricKey(header.alg, secretOrPrivateKey);
    } catch (error) {
      return failure(error);
    }
  }

  const timestamp = payload.iat || Math.floor(Date.now() / 1000);

  if (options.noTimestamp) {
    delete payload.iat;
  } else if (isObjectPayload) {
    payload.iat = timestamp;
  }

  if (typeof options.notBefore !== 'undefined') {
    try {
      payload.nbf = timespan(options.notBefore, timestamp);
    }
    catch (err) {
      return failure(err);
    }
    if (typeof payload.nbf === 'undefined') {
      return failure(new Error('"notBefore" should be a number of seconds or string representing a timespan eg: "1d", "20h", 60'));
    }
  }

  if (typeof options.expiresIn !== 'undefined' && typeof payload === 'object') {
    try {
      payload.exp = timespan(options.expiresIn, timestamp);
    }
    catch (err) {
      return failure(err);
    }
    if (typeof payload.exp === 'undefined') {
      return failure(new Error('"expiresIn" should be a number of seconds or string representing a timespan eg: "1d", "20h", 60'));
    }
  }

  Object.keys(options_to_payload).forEach(function (key) {
    const claim = options_to_payload[key];
    if (typeof options[key] !== 'undefined') {
      if (typeof payload[claim] !== 'undefined') {
        return failure(new Error('Bad "options.' + key + '" option. The payload already has an "' + claim + '" property.'));
      }
      payload[claim] = options[key];
    }
  });

  const encoding = options.encoding || 'utf8';

  if (typeof callback === 'function') {
    callback = callback && once(callback);

    jws.createSign({
      header: header,
      privateKey: secretOrPrivateKey,
      payload: payload,
      encoding: encoding
    }).once('error', callback)
      .once('done', function (signature) {
        // TODO: Remove in favor of the modulus length check before signing once node 15+ is the minimum supported version
        if(!options.allowInsecureKeySizes && /^(?:RS|PS)/.test(header.alg) && signature.length < 256) {
          return callback(new Error(`secretOrPrivateKey has a minimum key size of 2048 bits for ${header.alg}`))
        }
        callback(null, signature);
      });
  } else {
    let signature = jws.sign({header: header, payload: payload, secret: secretOrPrivateKey, encoding: encoding});
    // TODO: Remove in favor of the modulus length check before signing once node 15+ is the minimum supported version
    if(!options.allowInsecureKeySizes && /^(?:RS|PS)/.test(header.alg) && signature.length < 256) {
      throw new Error(`secretOrPrivateKey has a minimum key size of 2048 bits for ${header.alg}`)
    }
    return signature
  }
};

解決方法

• HS256のままでssh-keygenで生成した鍵を使わず、ランダムな文字列を扱う。
• RS256を利用し、対象鍵を利用する。