Unable to retrieve a cookie set by another application on the same domain
Is there any way I can get around this without resorting to my own PHP in the template or a custom plugin?


You can't have PHP is a Twig template, but I think you'd need a real simple plugin for this.

It would just have an init() method that did:

craft()-&gt;request-&gt;enableCookieValidation = false;


Just be aware that's going to make it much easier for people to potentially tamper with cookie values.