This is an enclosing shortcode. It returns an HTML link for authorization with Discord profile. You can set shortcode attributes to alter its behavior.
Content of shortcode - is a text of the link. If text is not set the default display will switch between Logout and Login with Discord texts.
You can enable Discord styling for this authorization and comments buttons in the WordPress admin panel go to Settings --> Discord and scroll down to Settings section. In Styling subsection you have the option to add styling to authorization buttons.