Drawbacks of Open Source
I recently re-investigated the PEAR LiveUser package - it wasn’t suitable for “grab and use” a year ago - and I was surprised to see that the changelog for this package is 4 years long! Come on, guys! What’s taking you so long?
At least there’s now installation instructions for it 
But really, sometimes it’s quicker to re-invent the wheel and have your custom authentication system done i two days and reuse it - getting accustomed with LiveUser’s documentation and API would take a comparable amount of time - and bugs you’ll find will be yours bugs, not the ones in highly complex code written by an alien team of people.