How to use the sshpk.PrivateKey function in sshpk

async.eachLimit(records, 10,function(record, recordCb) {
                        for (filter in callObj.filterKey){
                            if(callObj.filterConfig && callObj.filterConfig[filter]) {
                                parameters[callObj.filterKey[filter]] = OracleConfig[callObj.filterValue[filter]];
                            } else {
                                parameters[callObj.filterKey[filter]] = record[callObj.filterValue[filter]];
                            }
                        }

                        try {
                            OracleConfig.privateKey = sshpk.parsePrivateKey(OracleConfig.keyValue, 'pem');
                            assert.ok(sshpk.PrivateKey.isPrivateKey(OracleConfig.privateKey, [1, 2]),
                                'options.key must be a sshpk.PrivateKey');
                            (!OracleConfig.RESTversion ? OracleConfig.RESTversion = '/20160918' : false )
                        } catch (e) {
                            console.log('Could not read the Oracle Private Key.');
                        }
                        if (callObj.restVersion ||
                            callObj.restVersion == '') {
                            OracleConfig.RESTversion = callObj.restVersion;
                        };

                        oci(callObj.api, oracleService, callKey, OracleConfig, parameters, function(result) {
                            if (result.code) {
                                aggregatedErrors.push(result);
                            }
                            //console.log('\n' + require('util').inspect(result, {depth: null}));
                            if (result &&

var signature;
    if (alg[0] === 'hmac') {
      if (typeof (options.key) !== 'string' && !Buffer.isBuffer(options.key))
        throw (new TypeError('options.key must be a string or Buffer'));

      var hmac = crypto.createHmac(alg[1].toUpperCase(), options.key);
      hmac.update(stringToSign);
      signature = hmac.digest('base64');

    } else {
      var key = options.key;
      if (typeof (key) === 'string' || Buffer.isBuffer(key))
        key = sshpk.parsePrivateKey(options.key);

      assert.ok(sshpk.PrivateKey.isPrivateKey(key, [1, 2]),
        'options.key must be a sshpk.PrivateKey');

      if (!PK_ALGOS[key.type]) {
        throw (new InvalidAlgorithmError(key.type.toUpperCase() + ' type ' +
          'keys are not supported'));
      }

      if (alg[0] !== undefined && key.type !== alg[0]) {
        throw (new InvalidAlgorithmError('options.key must be a ' +
          alg[0].toUpperCase() + ' key, was given a ' +
          key.type.toUpperCase() + ' key instead'));
      }

      var signer = key.createSign(alg[1]);
      signer.update(stringToSign);
      var sigObj = signer.sign();

*/
    this.rs_signer = crypto.createHmac(alg[1].toUpperCase(), options.key);
    this.rs_signer.sign = function () {
      var digest = this.digest('base64');
      return ({
        hashAlgorithm: alg[1],
        toString: function () { return (digest); }
      });
    };

  } else if (options.key !== undefined) {
    var key = options.key;
    if (typeof (key) === 'string' || Buffer.isBuffer(key))
      key = sshpk.parsePrivateKey(key);

    assert.ok(sshpk.PrivateKey.isPrivateKey(key, [1, 2]),
      'options.key must be a sshpk.PrivateKey');
    this.rs_key = key;

    assert.string(options.keyId, 'options.keyId');
    this.rs_keyId = options.keyId;

    if (!PK_ALGOS[key.type]) {
      throw (new InvalidAlgorithmError(key.type.toUpperCase() + ' type ' +
        'keys are not supported'));
    }

    if (alg[0] !== undefined && key.type !== alg[0]) {
      throw (new InvalidAlgorithmError('options.key must be a ' +
        alg[0].toUpperCase() + ' key, was given a ' +
        key.type.toUpperCase() + ' key instead'));
    }

*/
    this.rs_signer = crypto.createHmac(alg[1].toUpperCase(), options.key);
    this.rs_signer.sign = function () {
      var digest = this.digest('base64');
      return ({
        hashAlgorithm: alg[1],
        toString: function () { return (digest); }
      });
    };

  } else if (options.key !== undefined) {
    var key = options.key;
    if (typeof (key) === 'string' || Buffer.isBuffer(key))
      key = sshpk.parsePrivateKey(key);

    assert.ok(sshpk.PrivateKey.isPrivateKey(key, [1, 2]),
      'options.key must be a sshpk.PrivateKey');
    this.rs_key = key;

    assert.string(options.keyId, 'options.keyId');
    this.rs_keyId = options.keyId;

    if (!PK_ALGOS[key.type]) {
      throw (new InvalidAlgorithmError(key.type.toUpperCase() + ' type ' +
        'keys are not supported'));
    }

    if (alg[0] !== undefined && key.type !== alg[0]) {
      throw (new InvalidAlgorithmError('options.key must be a ' +
        alg[0].toUpperCase() + ' key, was given a ' +
        key.type.toUpperCase() + ' key instead'));
    }

*/
    this.rs_signer = crypto.createHmac(alg[1].toUpperCase(), options.key);
    this.rs_signer.sign = function () {
      var digest = this.digest('base64');
      return ({
        hashAlgorithm: alg[1],
        toString: function () { return (digest); }
      });
    };

  } else if (options.key !== undefined) {
    var key = options.key;
    if (typeof (key) === 'string' || Buffer.isBuffer(key))
      key = sshpk.parsePrivateKey(key);

    assert.ok(sshpk.PrivateKey.isPrivateKey(key, [1, 2]),
      'options.key must be a sshpk.PrivateKey');
    this.rs_key = key;

    assert.string(options.keyId, 'options.keyId');
    this.rs_keyId = options.keyId;

    if (!PK_ALGOS[key.type]) {
      throw (new InvalidAlgorithmError(key.type.toUpperCase() + ' type ' +
        'keys are not supported'));
    }

    if (alg[0] !== undefined && key.type !== alg[0]) {
      throw (new InvalidAlgorithmError('options.key must be a ' +
        alg[0].toUpperCase() + ' key, was given a ' +
        key.type.toUpperCase() + ' key instead'));
    }