I'm in the same boat (SaaS app in the health sector) and opted for Auth0 after using it a fair bit in the finance sector with work. I'd say start with that and

I'm in the same boat (SaaS app in the health sector) and opted for Auth0 after using it a fair bit in the finance sector with work. I'd say start with that and once your app outgrows it then you can roll out a solution of your own but I'd suggest you don't try to reinvent that particular wheel when you're starting out.