Use a custom template function for csrf protection

templates/signin.gohtml

@@ -9,7 +9,7 @@
           Welcome back!
         </h1>
         <form action="/signin" method="post">
-          {{.CSRFField}}
+          {{csrfField}}
           <div class="py-2">
             <label for="email" class="text-sm font-semibold text-gray-800">
               Email Address

templates/signup.gohtml

@@ -10,7 +10,7 @@
             Sign Up!
           </h1>
           <form action="/signup" method="post">
-            {{.CSRFField}}
+            {{csrfField}}
             <div>
               <label for="signupEmail" class="text-sm font-semibold text-gray-800">Email Address</label>
               <input name="email" id="signupEmail" type="email" placeholder="Email address" required autocomplete="email"