Spring Security Principal transformation

Question

Is there a way to transform a Spring Security Principal before it is injected in a RestController method?

Let's say I have defined the following class:

@RestController
public class MyController {
    @GetMapping("/test")
    public void getWithPrincipalA(@AuthenticationPrincipal PrincipalTypeA a) {
        ...
    }

    @GetMapping("/test")
    public void getWithPrincipalB(@AuthenticationPrincipal PrincipalTypeB b) {
        ...
    }
}

I know that these controller methods are ambiguous and I could do several things to solve that, but what I would rather do is transform the @AuthenticationPrincipal to some type I can define myself. The result would become something like:

@RestController
public class MyController {
    @GetMapping("/test")
    public void getWithTransformedPrincipal(@AuthenticationPrincipal MyTransformedPrincipal principal) {
        ...
    }
}

Now I basically could define a single controller for several different authentication principals, without having to change the API.

Any help would be appreciated :)

Answer 1

Too keep things simple and transparant you could simply transform the principal in your controller method and dispatch the generic principal from there.

@RestController
public class MyController {
    @GetMapping("/test")
    public void getWithTransformedPrincipal(@AuthenticationPrincipal Principal principal) {
        GenericPrincipal generic = PrincipalTransformer.transform(principal);
        doSomethingWithPrincipal(generic);
    }
}