feat(form): add required attribute

templates/login.html

@@ -3,8 +3,8 @@
 {% block content %}
 <form method="post" class=login>
 <table>
-<tr><td>Username</td><td><input type="text" name="username"></td></tr>
-<tr><td>Password</td><td><input type="password" name="password"></td></tr>
+<tr><td>Username</td><td><input type="text" name="username" required></td></tr>
+<tr><td>Password</td><td><input type="password" name="password" required></td></tr>
 </table>
 <input type="submit" value="Login">
 </form>