Expose composed middleware via getMiddleware().

CHANGELOG.md

@@ -9,6 +9,7 @@ The version headers in this history reflect the versions of Apollo Server itself
 - `apollo-engine-reporting`: **BEHAVIOR CHANGE**: If the error returned from the `engine.rewriteError` hook has an `extensions` property, that property will be used instead of the original error's extensions. Document that changes to most other `GraphQLError` fields by `engine.rewriteError` are ignored. [PR #2932](https://github.com/apollographql/apollo-server/pull/2932)
 - `apollo-engine-reporting`: **BEHAVIOR CHANGE**: The `engine.maskErrorDetails` option, deprecated by `engine.rewriteError` in v2.5.0, now behaves a bit more like the new option: while all error messages will be redacted, they will still show up on the appropriate nodes in a trace. [PR #2932](https://github.com/apollographql/apollo-server/pull/2932)
 - `apollo-engine-reporting`: **BEHAVIOR CHANGE**: By default, send no GraphQL variable values to Apollo's servers instead of sending all variable values. Adding the new EngineReportingOption `sendVariableValues` to send some or all variable values, possibly after transforming them. This replaces the `privateVariables` option, which is now deprecated. [PR #2931](https://github.com/apollographql/apollo-server/pull/2931)
+- `apollo-server-express`, `apollo-server-koa`, `apollo-server-hapi`: A new `getMiddleware` method, which accepts the same parameters as `applyMiddleware` with the exception of the `app`, has been added.  This allows implementors to obtain the composed middleware and "`use`" it within an existing `app`.  This was previously only possible by passing an `app` to `applyMiddleware` or reaching into Apollo Server internals, but `getMiddleware` should allow a more natural method and will hopefully resolve many issues raised around the previous pattern. [PR #2435](https://github.com/apollographql/apollo-server/pull/2435)
 
   > Note: In order to keep shipping all GraphQL variable values to Apollo Engine, pass in the option:
   >

docs/source/api/apollo-server.md

@@ -147,7 +147,7 @@ In `apollo-server`, the listen call starts the subscription server and passes th
   * `subscriptionsPath`: <`String`>
   * `server`: <[`http.Server`](https://nodejs.org/api/http.html#http_class_http_server)>
 
-## ApolloServer.applyMiddleware
+## `ApolloServer.applyMiddleware`
 
 The `applyMiddleware` method is provided by the `apollo-server-{integration}` packages that use middleware, such as hapi and express. This function connects ApolloServer to a specific framework.
 
@@ -193,6 +193,14 @@ app.use('*', jwtCheck, requireAuth, checkScope);
 server.applyMiddleware({ app, path: '/specialUrl' }); // app is from an existing express app. Mount Apollo middleware here. If no path is specified, it defaults to `/graphql`.
 ```
 
+## `ApolloServer.getMiddleware`
+
+Similar to the `applyMiddleware` method above, though rather than applying the composition of the various Apollo Server middlewares which comprise a full-featured Apollo Server deployment (e.g. middleware for HTTP body parsing, GraphQL Playground, uploads and subscriptions) the `getMiddleware` simply returns the middleware.
+
+The `getMiddleware` method takes the same arguments as `applyMiddleware` **except** `app` should not be passed.  Instead, the result of `getMiddleware` must be added as a middleware directly to an existing application (e.g. with `app.use(...)`).
+
+For example, for `apollo-server-express`, this means that rather than passing `applyMiddleware` an `app` which was already initiated from calling `express()`, and `applyMiddleware` "using" (i.e. `app.use`), the implementor will instead call `app.use(...)` on the result of `getMiddleware` with the same arguments.
+
 ## `gql`
 
 The `gql` is a [template literal tag](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals#Tagged_templates). Template literals were introduced in recent versions of ECMAScript to provide embedded expressions (i.e. `` `A string with interpolated ${variables}` ``) and template literal tags exist to provide additional functionality for what would otherwise be a normal template literal.