Add config setup to docs (#204)

examples/app-with-on-behalf-of-auth/README.md

@@ -2,14 +2,27 @@
 
 This plugin is an example of how to integrate OAuth2 authentication into a Grafana plugin.
 
-**Note:** This plugin requires Grafana 10.1 or later and the `externalServiceAuth` feature toggle must be enabled. This is an experimental feature.
+**Note:** This plugin requires Grafana 10.1 or later
 
 ## How to use
 
 This app allows you to do requests to the Grafana API as the plugin or on behalf of a user (by specifying the user ID). The plugin will then use the access token to do requests to the Grafana API.
 
 ![screenshot](./src/img/screenshot-showcase.png)
 
+## Grafana configuration
+
+This is an experimental feature, the `externalServiceAuth` feature toggle must be enabled. 
+
+Additionally, Grafana needs `auth.extended_jwt` to be enabled and configured. Set your audience and issuer to your base URL. Example:
+
+```ini
+[auth.extended_jwt]
+enabled = true
+expect_audience = http://localhost:3000/
+expect_issuer = http://localhost:3000/
+```
+
 ## Authentication flow
 
 The plugin uses the [JWT Bearer Assertion OAuth2 Extension](https://datatracker.ietf.org/doc/html/rfc7523) to authenticate users and obtain an access token that can be used to authorize requests against the Grafana API. To enable it, add the section below to your `plugin.json` file.