feat: add Google Sign-In with JWT auth and Neon DB persistence

internal/webapp/static/app.js

@@ -25,6 +25,9 @@ const els = {
   status: document.querySelector("#status-line"),
   error: document.querySelector("#error-line"),
   title: document.querySelector("#session-title"),
+  gSignIn: document.querySelector(".g_id_signin"),
+  userInfo: document.querySelector("#user-info"),
+  logoutButton: document.querySelector("#logout-button"),
 };
 
 const readinessClassMap = {
@@ -359,11 +362,48 @@ function evidenceBlock(evidence = []) {
   return `<section><h2>Evidence</h2><ul class="small-list">${evidence.map((item) => `<li>${escapeHTML(item.quote || item.id)}</li>`).join("")}</ul></section>`;
 }
 
+window.handleCredentialResponse = async (response) => {
+  try {
+    const res = await request("/api/v1/auth/google", {
+      method: "POST",
+      body: JSON.stringify({ id_token: response.credential }),
+    });
+    localStorage.setItem("tutor_token", res.token);
+    localStorage.setItem("tutor_user", JSON.stringify(res.user));
+    setStatus(`Signed in as ${res.user.email}`);
+    renderAuth();
+  } catch (err) {
+    showError(err.message);
+  }
+};
+
+function renderAuth() {
+  const user = JSON.parse(localStorage.getItem("tutor_user") || "null");
+  const token = localStorage.getItem("tutor_token");
+  if (user && token) {
+    els.gSignIn.style.display = "none";
+    els.userInfo.style.display = "block";
+    els.userInfo.textContent = user.email;
+    els.logoutButton.style.display = "inline-block";
+  } else {
+    els.gSignIn.style.display = "block";
+    els.userInfo.style.display = "none";
+    els.logoutButton.style.display = "none";
+  }
+}
+
+els.logoutButton.addEventListener("click", () => {
+  localStorage.removeItem("tutor_token");
+  localStorage.removeItem("tutor_user");
+  renderAuth();
+  setStatus("Signed out");
+});
+
 async function request(url, options = {}) {
-  const response = await fetch(url, {
-    headers: { "Content-Type": "application/json" },
-    ...options,
-  });
+  const token = localStorage.getItem("tutor_token");
+  const headers = { "Content-Type": "application/json" };
+  if (token) headers["Authorization"] = `Bearer ${token}`;
+  const response = await fetch(url, { headers, ...options });
   const body = await response.json();
   if (!response.ok) {
     throw new Error(body.error || `Request failed: ${response.status}`);
@@ -398,3 +438,5 @@ function escapeHTML(value) {
     .replaceAll('"', "&quot;")
     .replaceAll("'", "&#039;");
 }
+
+renderAuth();