code: function Strategy(options, verify) {
    ['domain',
      'clientID',
      'clientSecret',
      'callbackURL'].forEach(function (k) {
      if(!options[k]){
        throw new Error('You must provide the ' + k + ' configuration value to use passport-auth0.');
      }
    });
  
  
    this.options = xtend({}, options, {
      authorizationURL: 'https://' + options.domain + '/authorize',
      tokenURL:         'https://' + options.domain + '/oauth/token',
      userInfoURL:      'https://' + options.domain + '/userinfo',
      apiUrl:           'https://' + options.domain + '/api'
    });
  
    if (this.options.state === undefined) {
      this.options.state = true;
    }
  
    this._base = Object.getPrototypeOf(Strategy.prototype);
    this._base.constructor.call(this, this.options, verify);
  
    this.name = 'auth0';
  }
docs: `Strategy` constructor.
  
  
  @param {Object} options
  @param {Function} verify
  @api public