Xumm authentication plugin allows customers to sign in using their Xumm account. If your new customers don’t want to sign up with their email, they can use Xumm authentication instead. Installation Guide
Sign up for a Xumm Developer account, if you don't already have one.
Download the Xumm Authentication plugin zip archive.
Navigate to Configuration -> Local plugins
Upload the plugin archive using the "Upload plugin or theme" plugin.
Scroll down through the list of plugins to find the newly installed plugin. And click on the "Install" button to install the plugin.