Take into account X-Forwarded-* headers in embedded mode.

Useful if the container is used behind a proxy.

src/main/java/se/su/dsv/oauth2/EmbeddedConfiguration.java

@@ -1,8 +1,11 @@
 package se.su.dsv.oauth2;
 
+import org.springframework.boot.web.servlet.FilterRegistrationBean;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Profile;
+import org.springframework.core.Ordered;
+import org.springframework.web.filter.ForwardedHeaderFilter;
 import se.su.dsv.oauth2.admin.repository.ClientRepository;
 import se.su.dsv.oauth2.admin.repository.ClientRow;
 
@@ -15,6 +18,16 @@ import java.util.Optional;
 @Configuration
 @Profile("embedded")
 public class EmbeddedConfiguration {
+    /**
+     * This filter takes the `X-Forwarded-*` headers and updates the request to reflect the original HTTP request.
+     */
+    @Bean
+    public FilterRegistrationBean<ForwardedHeaderFilter> forwardedHeaderFilter() {
+        var filterRegistrationBean = new FilterRegistrationBean<>(new ForwardedHeaderFilter());
+        filterRegistrationBean.setOrder(Ordered.HIGHEST_PRECEDENCE);
+        return filterRegistrationBean;
+    }
+
     @Bean
     public ClientRepository clientRepository() {
         ArrayList<ClientRow> clients = new ArrayList<>();