code: function Dfp(credentials, config, refreshToken) {
  
    this.dfpUser = new DfpUser(
      config.networkCode,
      config.appName,
      config.version
    );
  
    this.dfpUser.setSettings({
      client_id: credentials.clientId,
      client_secret: credentials.clientSecret,
      refresh_token: refreshToken,
      redirect_url: credentials.redirectUrl,
    });
  }
docs: Calling this constructor instantiates the client to the DFP api.
  @class
  
  @param {Object} credentials  Credentials generated by DFP. Instructions in
  the README.
  @param {[type]} config       Configuration object. Instructions in the
  README.
  @param {[type]} refreshToken Refresh token to resume a session with DFP, as
  opposed to obraining a new one. Instructions
  in the README.