title: authentication in mobile app with azure functions
body: <p>I am trying to develop a <strong>serverless backend</strong> for my xamarin app. and for that I chose <strong>azure functions</strong>.
  Now I already know that <strong>Azure Mobile Apps</strong> provide an <strong>SDK</strong> for this purpose with which we can easily enable <strong>Authentication</strong> with multiple ways which are following
   1. Azure Active Directiry
   2. Facebook
   3. Google
   4. Microsoft
   5. Twitter</p>
  
  <p>Now I want to allow login with atleast 2 of these in my app, but I am not using azure mobile app as backend, instead I am using azure functions. So how can I achieve the same result with serverless?</p>
  
  <p><strong>Thanks in advance.</strong></p>