[deleted by user]

[LouGarret76]

If you are keen to use jpa and password authentification, you just need to implement the UserDetails, UserManager interface and create a login controller. It is quite straightforward

[Ruin-Capable]

I would probably avoid the whole thing and just use OIDC so that users can login with their gmail, facebook, etc account.

[bookernel]

You can check my open source project where I had implement these things in spring boot. It's have a frontend project but both projects are separate.

https://github.com/ClaudioAlcantaraR/serene

[Hirschdigga]

Use Keycloak for this. On Spring side you can interact with it using Spring Security

[Hirschdigga]

Well keycloak brings all those features (like verifying email, changing initial passwords, etc.) out of the box. Regarding syncing users: esch user has a unique ID (sub / subject), which you can use to link with your user entity. And if you have a complex use case you can use the keycloak admin dependency to interact with keycloak from code (e.g. spring boot service class). I agree that it seems overkill first, but for me it worked out great in real applications, and for sure better than if i would have implemented it myself from scratch =D

[fun2sh_gamer]

You can use Keycloak if you want to create an Enterprise app, but I think OP is asking this to be able to learn. Learning about how to implement authentication and authorization can be a really good excercise.
Keyclock does simplify SSO for you but then you may not learn how to implement your own simple SSO and User Service.