add auth javascript

public/js/auth.js

@@ -0,0 +1,75 @@
+async function submitAuthForm(endpoint, email, password, errorElement) {
+    errorElement.hidden = true;
+    errorElement.textContent = '';
+
+    const response = await fetch(endpoint, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        credentials: 'same-origin',
+        body: JSON.stringify({ email, password }),
+    });
+
+    if (response.ok) {
+        window.location.href = '/home';
+        return;
+    }
+
+    let message = 'Something went wrong';
+    try {
+        const body = await response.json();
+        if (body.error) {
+            message = body.error;
+        }
+    } catch (parseError) {
+        // fall through to generic message
+    }
+    errorElement.textContent = message;
+    errorElement.hidden = false;
+}
+
+async function logout() {
+    await fetch('/api/auth/logout', {
+        method: 'POST',
+        credentials: 'same-origin',
+    });
+    window.location.href = '/login';
+}
+
+document.addEventListener('DOMContentLoaded', () => {
+    const loginForm = document.getElementById('login-form');
+    if (loginForm !== null) {
+        const errorElement = document.getElementById('login-error');
+        loginForm.addEventListener('submit', async (submitEvent) => {
+            submitEvent.preventDefault();
+            const email = document.getElementById('email').value;
+            const password = document.getElementById('password').value;
+            await submitAuthForm(
+                '/api/auth/login',
+                email,
+                password,
+                errorElement,
+            );
+        });
+    }
+
+    const registerForm = document.getElementById('register-form');
+    if (registerForm !== null) {
+        const errorElement = document.getElementById('register-error');
+        registerForm.addEventListener('submit', async (submitEvent) => {
+            submitEvent.preventDefault();
+            const email = document.getElementById('email').value;
+            const password = document.getElementById('password').value;
+            await submitAuthForm(
+                '/api/auth/register',
+                email,
+                password,
+                errorElement,
+            );
+        });
+    }
+
+    const logoutButton = document.getElementById('logout');
+    if (logoutButton !== null) {
+        logoutButton.addEventListener('click', logout);
+    }
+});