I am running a wiki farm. Pre-MediaWiki 1.27, we used php session save path as a central session repo, and users could navigate through multiple wikis without logging out. now that sessions are stored in object cache, somehow the cache key are unconditionally determined by wfMemcKey, thus preventing us from sharing sessions. Although we can use shared cookie domain to keep user feeling logged in from client side, the sessions on the server side are, in fact, different in every wiki.
As a consequence, if users open an edit tab on wiki Foo, then click any page on wiki Bar in another browser tab, and then again hit the save button on wiki Foo, they will be alerted with loss of session.
Is it possible to add a configuration variable that allows us to customize session cache key, or at least allow us to use wfGlobalCacheKey as the key builder?