Merge pull request #186 from Netflix/spring-graphql-docs

Update docs with request/response interceptor.

docs/advanced/intercepting-http-request-response.md

@@ -0,0 +1,23 @@
+# Response Instrumentation
+The DGS framework internally uses [GraphQL Java] and [Spring for GraphQL].
+
+If you need to modify the HTTP request and response headers, you can leverage the `WebGraphQlInterceptor` in [Spring for GraphQL] (https://docs.spring.io/spring-graphql/reference/transports.html#server.interception) to accomplish this.
+This provides a hook to update the request and response headers based using the `GraphQLContext`
+
+#### Example:
+
+```java  
+@Component
+public class MyInterceptor implements WebGraphQlInterceptor {
+    @Override
+    public Mono<WebGraphQlResponse> intercept(WebGraphQlRequest request, Chain chain) {
+        String value = request.getHeaders().getFirst("myHeader");
+        request.configureExecutionInput((executionInput, builder) ->
+                builder.graphQLContext(Collections.singletonMap("myHeader", value)).build());
+        return chain.next(request).doOnNext((response) -> {
+            String value = response.getExecutionInput().getGraphQLContext().get("myContext");
+            response.getResponseHeaders().add("MyContext", value);
+        });
+    }
+}
+```

docs/spring-graphql-integration.md

@@ -148,6 +148,11 @@ You can turn on async behavior by setting the `dgs.graphql.spring.webmvc.asyncdi
 It is worth noting that with the Spring GraphQL integration, your MockMVC test set up does need to be updated.
 Since web request processing is now based on async dispatching mechanism, we now [require explicit handling for this](https://docs.spring.io/spring-framework/reference/testing/spring-mvc-test-framework/async-requests.html) in the test setup.
 
+### Modifying Response headers
+Previously, the DGS Framework offered a mechanism to add custom response headers based on the result of processing the GraphQL query using a special `DgsRestController.DGS_RESPONSE_HEADERS_KEY` key.
+This is no longer supported. 
+The recommended way forward is to use the `WebGraphQlInterceptor` in Spring for GraphQL as described [here](./advanced/intercepting-http-request-response.md))
+
 ## Known Gaps and Limitations
 At this time, we are lacking support for SSE based subscriptions which is available in the original DGS Framework. 
 This is on the roadmap and will be made available in the near future depending on support in spring-graphql. 

mkdocs.yml

@@ -31,7 +31,7 @@ nav:
     - Subscriptions: advanced/subscriptions.md
     - Interfaces and Unions: advanced/type-resolvers-for-abstract-types.md
     - Instrumentation (Tracing, Metrics): advanced/instrumentation.md
-    - Response Instrumentation for MVC: advanced/response-instrumentation.md
+    - Intercepting Http request and Response for MVC: advanced/intercepting-http-request-response.md
     - GraphQLContext : advanced/graphqlcontext-leveraging.md
     - Data Fetching Context: advanced/custom-datafetcher-context.md
     - Federated Testing: advanced/federated-testing.md