use csrf token for login

Author: rachelambda

src/templates/login.html

@@ -16,6 +16,7 @@
 <fieldset>
 <legend>Sign in</legend>
 <form action="" method="post" novalidate>
+  {{ form.csrf_token() }}
   {{ form.hidden_tag() }}
   <p>
     {{ form.username.label }}<br>
@@ -35,4 +36,4 @@
 </form>
 </fieldset>
 
-{% endblock %}
+{% endblock %}