code: function Strategy(options, verify) {
    if (typeof options == 'function') {
      verify = options;
      options = {};
    }
    if (!verify) throw new Error('local authentication strategy requires a verify function');
  
    this._apiKeyField = options.apiKeyField || 'apikey';
    this._apiKeyHeader = options.apiKeyHeader || 'apikey';
  
    passport.Strategy.call(this);
    this.name = 'apikey';
    this._verify = verify;
    this._passReqToCallback = options.passReqToCallback;
  }
docs: `Strategy` constructor.
  
  The local api key authentication strategy authenticates requests based on the
  credentials submitted through an HTML-based login form.
  
  Applications must supply a `verify` callback which accepts `username` and
  `password` credentials, and then calls the `done` callback supplying a
  `user`, which should be set to `false` if the credentials are not valid.
  If an exception occured, `err` should be set.
  
  Optionally, `options` can be used to change the fields in which the
  credentials are found.
  
  Options:
  - `apiKeyField`  field name where the apikey is found, defaults to _apiKey_
  - `apiKeyHeader`  header name where the apikey is found, defaults to _apiKey_
  - `passReqToCallback`  when `true`, `req` is the first argument to the verify callback (default: `false`)
  
  Examples:
  
  passport.use(new APIKeyStrategy(
  function(apikey, done) {
  User.findOne({ apikey: apikey }, function (err, user) {
  done(err, user);
  });
  }
  ));
  
  @param {Object} options
  @param {Function} verify
  @api public