Auth0 provide a 3rd party authentication service, as they point out this can have a lot of benefits (along with a few drawbacks). They have written a great tutorial on integrating Auth0 with the PHP Symfony framework here:
Do many people have experience using Auth0 to handle their authentication? I’ve never used them and am naturally sceptical about tying my platform to a 3rd party supplier I will have to pay. However it’s so frequent seeing a lot of expensive developer time wasted on an inferior inhouse solutions so is this worth a try?