I know the thread is a bit old but wanted to give some explanation on what's happening here.

If you'd like to customize your Feign requests, you can use a RequestInterceptor. This can be a custom implementation or you can reuse what's available in the Feign library, e.g. BasicAuthRequestInterceptor.

How to register it? Well, there are 2 ways to do it depending on how you use Feign.

If you're using plain Feign without Spring, then you gotta set the interceptor to the Feign builder. An example is here.

Feign.builder()
     .requestInterceptor(new MyCustomInterceptor())
     .target(MyClient.class, "http://localhost:8081");

If you're using Spring Cloud OpenFeign and you use the @FeignClient annotation to construct your clients, then you have to create a bean from your RequestInterceptor by either defining it as a @Component or as a @Bean in one of your @Configuration classes. Example here.

@Component
public class MyCustomInterceptor implements RequestInterceptor {
    @Override
    public void apply(RequestTemplate template) {
        // do something
    }
}

Also, you can check out one of my articles in this topic, maybe that clears it up better: Customizing each request with Spring Cloud Feign