Don't do everything custom
On web projects, you often come across this decision about whether you will use a freely available component, or whether you will make it custom. While there’s no one-size-fits-all answer, I can assure you that it isn’t a good idea to do it ALL custom.
You could spend your time and resources having your developers build a login system, but that isn’t what your project is about. The login system just the plumbing, and any time you spend building it from scratch is time not spent on your special sauce.