feat(outline): enable option for GitHub

Author: raisedadead

k3s/apps/outline/manifests/base/secrets/.secrets.env.sample

@@ -24,7 +24,15 @@ GOOGLE_CLIENT_ID=<your-google-client-id>
 GOOGLE_CLIENT_SECRET=<your-google-client-secret>
 
 # =============================================================================
-# OPTIONAL - Restrict to specific domain(s)
-# =============================================================================
-# Comma-separated list of allowed domains for signup
-# GOOGLE_ALLOWED_DOMAINS=freecodecamp.org
+# OPTIONAL - GitHub Integration (PR/Issue previews)
+# =============================================================================
+# Create GitHub App at: https://github.com/settings/apps
+# Callback URL: https://outline.freecodecamp.net/api/github.callback
+# Enable "Request user authorization (OAuth) during installation"
+# Disable webhooks (not needed for previews)
+# Base64 encode private key: openssl base64 -in private-key.pem -out key-b64.txt
+GITHUB_CLIENT_ID=<from-github-app>
+GITHUB_CLIENT_SECRET=<generated-client-secret>
+GITHUB_APP_NAME=<last-part-of-public-link>
+GITHUB_APP_ID=<from-github-app-settings>
+GITHUB_APP_PRIVATE_KEY=<base64-encoded-private-key>