feature: Add delegate option to cors middleware (#3613)

* feature: Add delegate option to cors middleware

* Add CHANGELOG.md for #3613.

Co-authored-by: Jesse Rosenberger <git@jro.cc>

CHANGELOG.md

@@ -6,6 +6,8 @@ The version headers in this history reflect the versions of Apollo Server itself
 
 > The changes noted within this `vNEXT` section have not been released yet.  New PRs and commits which introduce changes should include an entry in this `vNEXT` section as part of their development.  When a release is being prepared, a new header will be (manually) created below and the the appropriate changes within that release will be moved into the new section.
 
+- Move TContext generic from requestDidStart method to ApolloServerPlugin Interface [#3525](https://github.com/apollographql/apollo-server/pull/3525)
+- `apollo-server-express`: Support `CorsOptionsDelegate` type on `cors` parameter to `applyMiddleware`, to align with the supported type of the underlying [`cors`](https://npm.im/cors) middleware [itself](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/31483b781ac30f98bdf4d40a517e921f2fc2ce37/types/cors/index.d.ts#L32). [PR #3613](https://github.com/apollographql/apollo-server/pull/3613)
 - `apollo-server-core`: Allow asynchronous initialization of datasources: the `initialize` method on datasources may now return a Promise, which will be settled before any resolvers are called. [#3639](https://github.com/apollographql/apollo-server/pull/3639)
 
 ### v2.9.16

packages/apollo-server-express/src/ApolloServer.ts

@@ -24,7 +24,7 @@ export { GraphQLOptions, GraphQLExtension } from 'apollo-server-core';
 
 export interface GetMiddlewareOptions {
   path?: string;
-  cors?: corsMiddleware.CorsOptions | boolean;
+  cors?: corsMiddleware.CorsOptions | corsMiddleware.CorsOptionsDelegate | boolean;
   bodyParserConfig?: OptionsJson | boolean;
   onHealthCheck?: (req: express.Request) => Promise<any>;
   disableHealthCheck?: boolean;