@EnableFeignClients
@SpringBootApplication
@RequiredArgsConstructor
public class DemoApplication implements CommandLineRunner {

    // Only actual necessary code that matters: the request interceptor
    public static class MyInterceptor implements RequestInterceptor {

        @Setter
        private Optional<FeignClientEncodingProperties> properties;

        @Override
        public void apply(RequestTemplate template) {
            final var encodingAppliedRequest = template.headers().get(HttpEncoding.ACCEPT_ENCODING_HEADER);
            final var encodingDesiredRequest = properties.map(e -> List.of(e.getContentEncodingTypes())).orElse(List.of());
            System.out.println("Encoding in use: " + encodingAppliedRequest);
            System.out.println("Encoding desired: " + encodingDesiredRequest);
        }
    }

    // All other code to make things work

    private final GithubClient client;

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        client.getIssues();
    }

    @RequiredArgsConstructor
    public static class MyCapability implements Capability {

        private final Optional<FeignClientEncodingProperties> properties;

        @Override
        public RequestInterceptor enrich(RequestInterceptor requestInterceptor) {
            if (requestInterceptor instanceof MyInterceptor myInterceptor)
                myInterceptor.setProperties(properties);
            return requestInterceptor;
        }
    }

}

@Configuration
class FeignConfiguration {

    @Bean
    Client client() {
        return new ApacheHttpClient();
    }

    @Bean
    Capability feignOAuthTokenCapability(Optional<FeignClientEncodingProperties> properties) {
        return new DemoApplication.MyCapability(properties);
    }
}

@FeignClient(name = "github", url = "https://github.com/spring-cloud/spring-cloud-openfeign")
interface GithubClient {

    @GetMapping("/issues")
    String getIssues();
}

@SpringBootTest
@ExtendWith(MockitoExtension.class)
class DemoApplicationTests {

    @Autowired
    private FeignClientEncodingProperties properties;

    @Autowired
    private FeignAcceptGzipEncodingInterceptor interceptor;

    @Test
    void terstInterceptorContainsEncodingFromProperties() {
        final var encodingApplied = new AtomicReference<>(List.<String>of());
        final var template = mock(RequestTemplate.class);
        when(template.header(eq(HttpEncoding.ACCEPT_ENCODING_HEADER), any(String[].class))).thenAnswer(invocation -> {
            encodingApplied.set(List.of((String[]) invocation.getRawArguments()[1]));
            return null;
        });
        interceptor.apply(template);

        final var encodingFromProperties = List.of(properties.getContentEncodingTypes());
        assertEquals(encodingFromProperties.toString(), encodingApplied.get().toString());
    }
}