diff --git a/src/public/layouts/layout.eta b/src/public/layouts/layout.eta
index ab5d0e6..952757c 100644
--- a/src/public/layouts/layout.eta
+++ b/src/public/layouts/layout.eta
@@ -24,6 +24,10 @@
         } else {
             gtag('consent', 'default', JSON.parse(localStorage.getItem('consentMode')));
         }
+
+        if(localStorage.getItem('userId') != null) {
+            window.dataLayer.push({'user_id': localStorage.getItem('userId')});
+        }
     </script>
     <!-- Google Tag Manager -->
     <script>(function (w, d, s, l, i) {
@@ -46,10 +50,12 @@
     
     <%~ it.body %>
 
+    <%~ includeFile("debug")  %>
+
     <%~ includeFile("consent")  %>
 
     <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.2.2/dist/js/bootstrap.bundle.min.js"
         integrity="sha384-OERcA2EqjJCMA+/3y+gxIOqMEjwtxJY7qPCqsdltbNJuaOe923+mo//f6V8Qbsw3"
         crossorigin="anonymous"></script>
 </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/src/public/login.eta b/src/public/login.eta
new file mode 100644
index 0000000..39833a7
--- /dev/null
+++ b/src/public/login.eta
@@ -0,0 +1,83 @@
+<% layout("layout", { title: "Login - GA Tutorials" }) %>
+    
+<%~ includeFile("nav") %>
+
+<main class="container-lg pt-3">
+    <h1>Simulate login to set User ID</h1>
+    <form id="login-form">
+        <div class="form-group">
+            <label for="user-id">GA4 User ID</label>
+            <input type="text" class="form-control" id="user" name="user-id" aria-describedby="userIdHelp"
+                placeholder="Enter User ID">
+            <small id="userIdHelp" class="form-text text-muted">This form simply
+            sets your User ID so tagging will include it in events. To log out, submit
+            the form without a value.</small>
+        </div>
+        <button type="submit" id="btn-login" class="btn btn-primary">Submit</button>
+        <button type="button" id="gen-id" class="btn btn-info">Generate ID</button>
+        <button type="button" id="btn-logout" class="btn btn-warning">Log out</button>
+    </form>
+</main>
+
+<script>
+  
+    document.getElementById('btn-login').addEventListener('click', function() {
+        loginUserId(document.getElementById('user').value);
+    });
+
+    function loginUserId(userId) {
+        // Sets 'userId' in storage so layout.eta can set this in the dataLayer on
+        // each page.
+        localStorage.setItem('userId', userId);
+    }
+
+    document.getElementById('btn-logout').addEventListener('click', function() {
+        logout(document.getElementById('user'));
+    });
+
+    function logout(userIdField) {
+        localStorage.removeItem('userId');
+        userIdField.value = null;
+    }
+
+    document.getElementById('gen-id').addEventListener('click', function() {
+        generateUserId(document.getElementById('user'));
+    });
+
+    function generateUserId(userField) {
+        const prefixes = [
+            'doubloons',
+            'oceanographer',
+            'retrogressed',
+            'unmistakably',
+            'counterbalanced',
+            'wainscottings',
+            'servomechanism',
+            'expressionist',
+            'preciousness',
+            'fossilization',
+            'conglomerated',
+            'anthropomorphism',
+            'reappointment',
+            'transfigures',
+            'choreographer',
+            'sophisticated',
+            'calibrations',
+            'propitiating',
+            'effortlessly',
+            'prioritizing',
+            'rechargeable',
+            'thermostatic',
+            'acclimatization',
+        ];
+        const randIndex = Math.floor(Math.random() * prefixes.length);
+        const randId = Math.floor(Math.random() * 1000 * 1000 * 1000 * 1000);
+        userField.value = prefixes[randIndex] + '-' + randId;
+    }
+
+    window.onload = () => document.getElementById('user').value = localStorage.getItem('userId');
+  
+</script>
+
+<%~ includeFile("footer.eta") %>
+ 
\ No newline at end of file
diff --git a/src/public/newsletter.eta b/src/public/newsletter.eta
index cea8ff9..8de1a82 100644
--- a/src/public/newsletter.eta
+++ b/src/public/newsletter.eta
@@ -6,7 +6,7 @@
     <h1>Signup for our Newsletter</h1>
     <form id="newsletter-form" action="/thank-you">
         <div class="form-group">
-            <label for="exampleInputEmail1">Email address</label>
+            <label for="email">Email address</label>
             <input type="email" class="form-control" id="email" name="email" aria-describedby="emailHelp"
                 placeholder="Enter email">
             <small id="emailHelp" class="form-text text-muted">This form does not save your email. It is for the
diff --git a/src/public/partials/debug.eta b/src/public/partials/debug.eta
new file mode 100644
index 0000000..91ff977
--- /dev/null
+++ b/src/public/partials/debug.eta
@@ -0,0 +1,75 @@
+<div class="container-sm">
+  <button class="btn btn-info" type="button" data-bs-toggle="collapse" data-bs-target="#debug-panel" aria-expanded="true" aria-controls="debug-panel">Toggle debug panel</button>
+  <!-- Collapsible debug panel -->
+  <div class="collapse" id="debug-panel">
+      <button id="btn-fetch" class="btn btn-outline-primary">Fetch debug values</button>
+      <button id="btn-clear" class="btn btn-outline-warning">Clear client and session</button>
+      <br/>
+      <label for="tag-id">GA4 Tag ID</label>
+      <input type="text" class="form-control" id="tag-id" name="tag-id" disabled="true">
+      <label for="session-id">GA4 Session ID</label>
+      <input type="text" class="form-control" id="session-id" name="session-id" disabled="true">
+      <label for="client-id">GA4 Client ID</label>
+      <input type="text" class="form-control" id="client-id" name="client-id" disabled="true">
+      <label for="user-id">GA4 User ID</label>
+      <input type="text" class="form-control" id="user-id" name="user-id" disabled="true">
+  </div>
+</div>
+
+<script>
+  // Function for populating the debug panel values.
+  function setIds() {
+    // TODO: This may not be a reliable solution. From:
+    //       https://stackoverflow.com/questions/76075126/given-gtm-installed-ga4-how-to-send-events-via-gtag-without-send-to
+    var gtagIds = Object.keys( window.google_tag_manager || [] ).filter( e => { return e.substring(0,2) == 'G-' } );
+    if (gtagIds) {
+      // Uses the first tag ID found.
+      const firstTagId = gtagIds[0];
+
+      // Gets each field that will be updated.
+      const tagIdField = document.getElementById('tag-id');
+      const sessionIdField = document.getElementById('session-id');
+      const clientIdField = document.getElementById('client-id');
+      const userIdField = document.getElementById('user-id');
+
+      Promise.all([
+        firstTagId,
+        localStorage.getItem('userId'),
+        // Gets values from gtag.
+        // See https://developers.google.com/tag-platform/gtagjs/reference#set_examples.
+        new Promise(cid => gtag('get', firstTagId, 'client_id', cid)),
+        new Promise(sid => gtag('get', firstTagId, 'session_id', sid)),
+      ]).then(([tagId, userId, clientId, sessionId]) => {
+        // Updates value for each field.
+        tagIdField.value = tagId;
+        userIdField.value = userId;
+        clientIdField.value = clientId;
+        sessionIdField.value = sessionId;
+
+        // Logs info as an object.
+        console.log(JSON.stringify(
+          {
+            "user_id": userIdField.value,
+            "client_id": clientId,
+            "session_id": sessionId,
+          },
+          null,
+          '  '));
+      });
+    }
+  }
+  document.getElementById('btn-fetch').addEventListener("click", setIds);
+
+  // Function for clearing the GA cookies.
+  function clearCookies() {
+    document.cookie.split('; ').map(c => c.split('=')[0]).forEach(
+      name => document.cookie = name + '=; expires=Thu, 01 Jan 1970 00:00:01 GMT;');
+    // Reloads the page.
+    location.reload();
+  }
+  document.getElementById('btn-clear').addEventListener("click", clearCookies);
+
+  // Populates the debug panel when shown.
+  document.getElementById('debug-panel').addEventListener('shown.bs.collapse', event =>
+    setIds());
+</script>
diff --git a/src/public/partials/footer.eta b/src/public/partials/footer.eta
index 0b58f19..0f0db21 100644
--- a/src/public/partials/footer.eta
+++ b/src/public/partials/footer.eta
@@ -23,7 +23,7 @@
                         <h5>Subscribe to our newsletter</h5>
                         <p>This is a demo and does not save your email.</p>
                         <div class="d-flex flex-column flex-sm-row w-100 gap-2">
-                            <label for="newsletter1" class="visually-hidden">Email address</label>
+                            <label for="email" class="visually-hidden">Email address</label>
                             <input id="email" name="email" type="text" class="form-control" placeholder="Email address">
                             <button class="btn btn-primary" type="submit">Subscribe</button>
                         </div>
diff --git a/src/public/partials/nav.eta b/src/public/partials/nav.eta
index 6d56cdd..30cb114 100644
--- a/src/public/partials/nav.eta
+++ b/src/public/partials/nav.eta
@@ -15,6 +15,9 @@
                 <li class="nav-item">
                     <a class="nav-link" href="/profile">Profile</a>
                 </li>
+                <li class="nav-item">
+                    <a class="nav-link" href="/login">Login</a>
+                </li>
             </ul>
         </div>
     </div>