RegistrationApi.java

public sealed interface RegistrationApi {

	@Post
	HttpResponse<URI> registerUser(RegisterUserRequest request);

	non-sealed interface RegistrationClient extends RegistrationApi {}

	@Controller("/api/registration")
	@Secured(SecurityRule.IS_ANONYMOUS)
	final class RegistrationController implements RegistrationApi {

		private final RegistrationService registrationService;

		public RegistrationController(RegistrationService registrationService) {
			this.registrationService = registrationService;
		}

		@Override
		public HttpResponse<URI> registerUser(RegisterUserRequest request) {
			final var id = this.registrationService.createRegistration(request);
			if (id != null) {
				return HttpResponse.created(URI.create("/api/users/" + id));
			}
			return HttpResponse.status(HttpStatus.BAD_REQUEST, "User already exists");
		}
	}
}