Yes you can, you can either create login on some http server which will some how send it to game server some session id some how or use UE4 replication by using function call replcation
Alternatively you can throw out this all together and use OnlineSubsystem which utilize online service (like Steam, Facebook as well as PSN and XboxLive on consoles) authentication system, then all user need to do is to be logged in to one of them and then on UE4 server, then you simply use online service unique ID that that service provide to identify user. This is easiest option.
Either way you pick, you are forced to use C++… well maybe HTTP option can done in blueprint with VaRest plugin
You question is quite general so, ask something more specific, maybe pick one of the options that sounds suitable for you