Below link will help to set up/ context for the application security where a UI application is accessing this API https://www.baeldung.com/spring-security-auth0 https://hantsy.github.io/blog/2021/secures-rest-apis-with-spring-security-5-and-auth0/ https://www.toptal.com/spring/spring-security-tutorial
For M2M setup refer the below link: https://auth0.com/docs/quickstart/backend/java-spring-security5?download=true
It is preferable to refer the Auth0 documentation to understand how to do it correctly https://auth0.com/docs/quickstarts