ErrorException: ini_set() A session is active.

Thanks for your help. Ultimately it seems like it's going to be easier for me to just maintain multiple files until we get to the point where we can rid ourselves of the other environment. Thankfully, it appears that, since our other environment controls the login process (technically a combined CI2 [yes, it's old] and pure php), it somehow automagically creates a $_COOKIE variable with the information I need to pull from on the CI4 side to validate the login.