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Setting up a Spring Boot resource server is pretty straightforward. In fact, all you need is the Okta Spring Boot starter in your dependencies. You can even use the Okta Maven Plugin to create your account and configure Spring Boot.
Then, on the Angular side, you just need an interceptor that adds your access token to the Authorization header.
This blog post might help: https://developer.okta.com/blog/2020/01/06/crud-angular-9-spring-boot-2