For authentication I use Auth0 on the free tier, with a passwordless setup that uses Google OAuth and Microsoft OAuth and allows fallback to emailing a code to a user. We store nothing more than the email address. The great thing about Auth0 is the separation it provides between the authentication layer and the web app, and how if you go down the SaaS route you can allow people to bring their own Auth0 accounts and configure their own bespoke authentication.

For authorization you are going to have to implement your own solution once you have an authenticated session. What someone can do always depends on your app and the functions you provide and so there is no nice third party solution to this. In my case I store the map of users to roles and what a role can do in a PostgreSQL app and cache there the answers to "which users are in a role" and "what can a role do"... user permission and roles changes are infrequent but flush the cache and so take immediate effect.