Quarkus offers an integration with OpenIdConnect (OIDC). This means, you can use indentity providers like Keycloak, ForgeRock or AWS Cognito to delegate your authentication needs. With Keycloak, you can also have identity brokering with other identity providers. This means, people can sign up with your application/service via Keycloak directly or people can also select an option like "Login with GitHub".
For the general usage of OIDC with Quarkus, please refer to this guide. My post is about the specific need of offering a Login-button in your application; which I would have thought to be an out of the box feature. Don’t get me wrong; this is not hard to achieve, but also not trivial and well documented.
My general setup is a Quarkus application with server-side-rendered Web frontend. This may be JSF (the Quarkus Universe offers a MyFaces extension), but for me it was using the more lightweight Qute template library; which feels more like Spring MVC with Thymeleaf.