title: How can i secure my Firebase "subscribe to topic" from the web client?
body: <p>In firebase FCM i can subscribe to a topic through the web client like this:</p>
  
  <pre><code>curl -X POST -H "Authorization: key=&lt;your_server_key&gt;" -H "Content-Type: application/json" -H "Content-Length: 0" "https://iid.googleapis.com/iid/v1/&lt;your_instance_token&gt;/rel/topics/&lt;topic_name&gt;"
  </code></pre>
  
  <p>The only usage i have form Firebase is sending push notifications form the server to web clients that are subscribed to a specific topic.</p>
  
  <p>But how can i prevent unwanted people from subscribing to my topics?</p>