How to authenticate with the Email Signature web add-in in Outlook?

This article explains how to authenticate with the Email Signature web add-in Outlook as an end-user.

Go to Outlook application (Outlook Online in the browser or Outlook desktop on Mac)
Note for Outlook Online: Sign in to your Microsoft 365 account if you're not already.
Go to "New message" and click on the sign-in link shown below:
If you're already signed in, Templafy task pane will launch and you can see your available signatures. If you're not logged in, you will be prompted with a sign-in flow

Your default user profile will always display on top if you have multiple user profiles and it's marked with a star next to it. The default user profile will be pre-selected in New and Reply & Forward, which means you will have to actively select another user profile when you e.g. reply to an email if you don't want to use your default one.