Ask HN: SaaS product for account management in my app (billing, invites, etc)?

Earlier today, my coworker was trying to setup accounts for a new SaaS service we just started using. I have the billing information and only admins can modify billing information, so she tried to figure out how to make me an admin. Turns out, the service only supports a single admin and you need to be an admin to modify billing and invite team members to join the account.

This is one recent example of a million SaaS services that I have used which do not support seemingly basic account management capabilities such as inviting teammates, controlling licenses/billing, etc.

It seems to me like every company/startup out there is constantly reinventing the wheel (often poorly) when it comes to these basic account management capabilities. It would make sense to me if someone started a company which literally just offered these account management boilerplate capabilities as a SaaS product somehow.

Does anyone know if such a thing exists? If it doesn't, can anyone think of reasons it doesn't exist? Would you use such a service so that you can focus on creating your product instead of the (necessary) boilerplate functionality relating to accounts, billing, etc, etc?