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.