move docs to the microsite

plugins/proxy-backend/README.md

@@ -1,6 +1,7 @@
 # Proxy backend plugin
 
-This is the backend plugin that enables proxy definitions to be declared in and read from app-config.yaml.
+This is the backend plugin that enables proxy definitions to be declared in,
+and read from, `app-config.yaml`.
 
 Relies on the `http-proxy-middleware` package.
 
@@ -10,69 +11,22 @@ This backend plugin can be started in a standalone mode from directly in this pa
 with `yarn start`. However, it will have limited functionality and that process is
 most convenient when developing the plugin itself.
 
-To run it within the backend do:
-
-1. Register the router in `packages/backend/src/index.ts`:
-
-```ts
-const proxyEnv = useHotMemoize(module, () => createEnv('proxy'));
-
-const service = createServiceBuilder(module)
-  .loadConfig(configReader)
-  /** ... other routers ... */
-  .addRouter('/proxy', await proxy(proxyEnv, '/proxy'));
-```
-
-2. Start the backend
+The proxy is already installed in the Backstage backend per default, so you can also
+start up the full example backend to experiment with the proxy.
 
 ```bash
 yarn workspace example-backend start
 ```
 
-This will launch the full example backend.
-
 ## Configuration
 
-Example:
-
-```yaml
-# in app-config.yaml
-proxy:
-  '/simple-example': http://simple.example.com:8080
-  '/larger-example/v1':
-    target: http://larger.example.com:8080/svc.v1
-    headers:
-      Authorization:
-        $secret:
-          env: EXAMPLE_AUTH_HEADER
-```
-
-Each key under the proxy configuration entry is a route to match, below the prefix that the proxy
-plugin is mounted on. For example, if the backend mounts the proxy plugin as `/proxy`,
-the above configuration will lead to the proxy acting on backend requests to
-`/proxy/simple-example/...` and `/proxy/larger-example/v1/...`.
-
-The value inside each route is either a simple URL string, or an object on the format accepted by
-[http-proxy-middleware](https://www.npmjs.com/package/http-proxy-middleware).
-
-If the value is a string, it is assumed to correspond to:
-
-```yaml
-target: <the string>
-changeOrigin: true
-pathRewrite:
-  '^<url prefix><the string>/': '/'
-```
-
-When the target is an object, it is given verbatim to `http-proxy-middleware` except with the
-following caveats for convenience:
-
-- If `changeOrigin` is not specified, it is set to `true`. This is the most commonly useful value.
-- If `pathRewrite` is not specified, it is set to a single rewrite that removes the entire route. In the
-  above example, a rewrite of `'^/proxy/larger-example/v1/': '/'` is added. That means that a request to
-  `/proxy/larger-example/v1/some/path` will be translated to a request to
-  `http://larger.example.com:8080/svc.v1/some/path`.
+See [the proxy docs](https://backstage.io/docs/plugins/proxying).
 
 ## Links
 
+- [Call Existing API](https://backstage.io/docs/plugins/call-existing-api) helps the
+  decision process of what method of communication to use from a frontend plugin to
+  your API
+- [The proxy plugin documentation](https://backstage.io/docs/plugins/proxying) describes
+  configuration options and more
 - [http-proxy-middleware](https://www.npmjs.com/package/http-proxy-middleware)