README

Cross-link between pages with different domain names of a Contao installation—and keep certain cookies alive. It will be possible to handle a member authentication between multiple domains. Or the isotope cart.

Install

Via composer

$ composer require richardhj/contao-crossdomaincookies

Usage

• Make sure that all domains used in the Contao installation are set in the "dns" field of the root pages.
• The user has to click a link in order to fetch the cookies of the site (he/she originally logged in). Include the link with an InsertTag.

InsertTags

Make sure to replace 99 with the id or alias of the other page.

How it works

Page A and Page B are part of one Contao installation.

When hyperlinking from Page A to Page B, the link looks like https://page-b.local/?o=page-a.local&t=zyxitopjfsetbjjutwsdf

As you can see, two get parameters are added to the page uri:

When being on Page B—and the get parameters are present—, a javascript will be included. This script will create the cookies on Page B. The script will get loaded from https://page-a.local, therefore the cookies are the ones present on Page A.

The javascript looks like

document.cookie = "FE_USER_AUTH=; expires=Sun, 10 Sep 2017 17:34:31 GMT; path=/";
document.cookie = "FE_AUTO_LOGIN=abcdefghijklmnopqr; expires=Mon, 11 Dec 2017 17:34:31 GMT; path=/";

That's the magic behind cross domain cookies.

Security

A few words about the security and vulnerability:

The extension automatically loads a javascript from a site that is given as a get parameter. The get parameter can be easily modified and this extension would be a great example for XSS-vulnerably in practice. So this extension needs to check that the url given as get parameter is part of the Contao installation. So before including the javascript from the other domain, it verifies that the other domain can be found in the "dns" fields of the root pages of the Contao installation.

In order to handle the authentication cross-domain, this extension activates auto_login ("Remember me") for the particular user. That means, that the user will not get logged out by closing the window, which is the default behavior. This is because Contao checks the auth cookie against the session_id which is bound to a cookie as well and will therefore change on the other domain. This might be a problem for websites with sensible data and users who forget to log out. To keep the problem down, the auto_login cookie will expire after a few time.

License

The GNU Lesser General Public License (LGPL).

Feel free to contribute.