add more examples for shared secrets

Author: sahansera

docs/auth_plugins.md

@@ -345,6 +345,13 @@ auth:
   header: Authorization
 ```
 
+```bash
+curl -X POST "https://your-hooks-server.com/webhooks/example" \
+  -H "Authorization: your-shared-secret" \
+  -H "Content-Type: application/json" \
+  -d '{"event":"test","data":"example"}'
+```
+
 **Custom header shared secret:**
 
 ```yaml
@@ -354,6 +361,14 @@ auth:
   header: X-API-Key
 ```
 
+```bash
+curl -X POST "https://your-hooks-server.com/webhooks/example" \
+  -H "X-API-Key: your-shared-secret" \
+  -H "Content-Type: application/json" \
+  -d '{"event":"test","data":"example"}'
+```
+
+
 ## Custom Auth Plugins
 
 This section provides an example of how to implement a custom authentication plugin for a hypothetical system. The plugin checks for a specific authorization header and validates it against a secret stored in an environment variable.