title: How to achieve login authentication in Excel add-in using OfficeJS
body: <p>We are using Excel add-in in OfficeJS and wanted to implement login authentication with below requirements.</p>
  
  <ol>
  <li>we have own on-premise server (identity),</li>
  <li>need to achieve access and refresh token.</li>
  </ol>
  
  <p>Kindly suggest any examples for the same.</p>