django.contrib.messages.storage.fallback.CookieStorage does not behave properly with subdomains

[Chris Lamb]

Imagine you have two domains "www.example.com" and "special.example.com". Your SESSION_COOKIE_DOMAIN is set to ".example.com" so that users are logged-in across these two subdomains.

The problem arises when a page on "www.example.com" sets a django.contrib.message and redirects to "special.example.com", the user will not see it unless they return to "www.example.com" as the default domain of the cookie is the current one. This naturally causes confusion as actions users have performed in the past suddenly are being confirmed (!).

This happens with FallbackStorage too as it wraps CookieStorage.

Patch attached that sets the domain of the CookieStorage cookie to SESSION_COOKIE_DOMAIN. Whilst this works, it might be better to not couple sessions and messages in this way, so we could alternatively introduce a new setting under a the MESSAGE_STORAGE_ namespace.

[Adrian Holovaty]

In [15848]:

Fixed #15618 -- CookieStorage storage in messages framework now honors SESSION_COOKIE_DOMAIN. Thanks for the report and patch, lamby

[Adrian Holovaty]

Note that I opted to use SESSION_COOKIE_DOMAIN here even though this technically isn't for django.contrib.sessions. I didn't want to add another setting, and I couldn't think of a case where you might want the cookie domain to be different for messages vs. sessions. Down the road we may want to rename SESSION_COOKIE_DOMAIN to COOKIE_DOMAIN.

[Chris Lamb]

Oops, we need to delete the cookie from the right domain too. Attaching patch.

[Julien Phalip]

Thanks for spotting this. See attached patch with the final fix and tests for the whole thing.

[Jannis Leidel]

In [15885]:

Fixed #15618 -- Fixed regression introduced in r15848 regarding not properly deleting messages cookies when honoring SESSION_COOKIE_DOMAIN. Thanks, Julien.