Authentication shortcode
mvanThis page describes you can add a Sign in with Microsoft link with corresponding functionality anywhere on your website. You can see this shortcode in action on our very own checkout page.
WordPress Extranet
If you want to turn your WordPress website into a WordPress Extranet and like to make (parts of) your WordPress website available to customers, partners or basically to any other user from another Microsoft Office 365 Azure AD tenant, you can do so now.