Add MFA link to the main page

Author: NhienLam

auth/index.html

@@ -58,6 +58,8 @@ <h2 class="mdl-card__title-text">Table of Contents</h2>
             <li><a href="email-password.html">Email and Password authentication</a></li>
             <li><a href="email-link.html">Email Link authentication</a><br><br></li>
 
+            <li><a href="mfa-password.html">SMS multi-factor authentication</a><br><br></li>
+
             <li><a href="customauth.html">Custom Authentication</a> and an Example <a href="exampletokengenerator/auth.html">Custom Token Generator</a><br><br></li>
 
             <li><a href="phone-visible.html">Phone number sign-in with visible ReCaptcha</a></li>