Add changeset for GitHub apps support

.changeset/clever-timers-thank.md

@@ -0,0 +1,25 @@
+---
+'@backstage/backend-common': patch
+'@backstage/integration': patch
+---
+
+Add support for Github Apps authentication for backend plugins.
+
+`GithubCredentialsProvider` requests and caches GitHub credentials based on a repository or organization url.
+
+The `GithubCredentialsProvider` class should be considered stateful since tokens will be cached internally.
+Consecutive calls to get credentials will return the same token, tokens older than 50 minutes will be considered expired and reissued.
+`GithubCredentialsProvider` will default to the configured access token if no GitHub Apps are configured.
+
+More information on how to create and configure a GitHub App to use with backstage can be found in the documentation.
+
+Usage:
+
+```javascript
+const credentialsProvider = new GithubCredentialsProvider(config);
+const { token, headers } = await credentialsProvider.getCredentials({
+  url: 'https://github.com/',
+});
+```
+
+Updates `GithubUrlReader` to use the GithubCredentialsProvider.