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

Answer 3

Wow, still relevant in 2020. Only thing that works for me is to leave cookie domains blank on both domain.com and dev.domain.com (I use non-www same as OP) and then set different backend admin urls via Custom Admin Path setting in admin. Obviously you have to do this via database if you can't access directly.

Anyone comment on the dangers of leaving cookie domain empty like I do? I do periodically have customers with login redirects, but it's not common and not sure if setting domains will help anyway.

Edit: domain.com and dev.domain.com seem to work fine in combination with my above answer using custom domain paths different for admins. Will update if any issues.