title: Parameters in Firebase Cloud Functions HTTPS
body: <p>How can I set some parameters on my HTTPS functions in Firebase? 
  I am building an app, and while building the app, I have managed to grow my mailing list. Now I want to send mails out, but I want to make sure that they can unsubscribe before I send anything out. </p>
  
  <p>I am using Firebase for everything, and I have managed to make a function that sends mails out to every subscribed mail.</p>
  
  <p>I am also able to "unsubscribe" a specific mail, but that is hardcoded, and not at all an optimal solution. </p>
  
  <pre><code>exports.testUnsub = functions.https.onRequest((req, res) =&gt; {
    var db = admin.database();
    var ref = db.ref("mailingList/-KhBOisltrOmv57Mrzus");
    ref.child("subscribed").set(false);
    console.log("-KhBOisltrOmv57Mrzus has unsubscribed from mailing list.");
  });
  </code></pre>
  
  <p>In the mail I send there is an URL, which triggers this HTTPS function. I want to set a parameter on that URL so it becomes dynamic. Something like:</p>
  
  <pre><code>https://us-central1-&lt;project-id&gt;.cloudfunctions.net/testUnsub?listID=xxxxxxxxxxx
  </code></pre>
  
  <p>I am looking for anything that can get me on the right direction.</p>