php中的简单授权/登录功能

I'm looking to implement user login onto my site for the first time. I'm happy to either build my own solution, or implement something open source, however no package has been an obvious choice in my search so far. Equally, I'm fully aware that as an intermediate php programmer at best, I am highly likely to miss something obvious if I roll my own solution, and leave the doors well and truly open.I'm looking to implement user login onto my sit