Dev/Staging/Live Cookie Domain For Non-www Sites

Question

The live URL is http://shop.com. The development/staging URL is http://sub.shop.com. How do I have to set up the cookie domain, so that I can log into both admin areas without any interdependencies? I tried the following cookie domain settings, but none of them worked:

Live cookie domain: .shop.com
Dev cookie domain: .shop.com
Result: Live login does not work.

Live cookie domain: shop.com
Dev cookie domain: .shop.com
Result: Logging out from one admin area means that you are also logged out from the other admin area.

Live cookie domain: shop.com
Dev cookie domain: sub.shop.com
Result: Dev login does not work.

Live cookie domain: .shop.com
Dev cookie domain: sub.shop.com
Result: No login works.

Live cookie domain: shop.com
Dev cookie domain: .sub.shop.com
Result: Dev login does not work.

Live cookie domain: .shop.com
Dev cookie domain: .sub.shop.com
Result: No login works.

Of course, I have disabled the Magento cache and I clear the cookies in my browser before trying each setting.

Answer 1

This looks pretty much like the login issue described by Phillip Jackson.

An adminhtml cookie must not be valid for more than one installation. If you can, use separate second-level domains for each of the sites or access the live admin area via subdomain.

Answer 2

My preferred setup is this

Live cookie domain: example.com
Dev cookie domain: test.example.com

However, it seems to work best if the live domain is not a "parent" of the dev domain, i.e.

Live cookie domain: www.example.com
Dev cookie domain: test.example.com