Two-factor (2-factor) authentication is optional for users in Passthrough to use as an additional security layer.
To enable this, click on the account icon in the top right corner of any page.
Then click on "Account settings."
Toggle to "Use a password for 2-step authentication" and create a password.
Please be sure to save your password somewhere safe for reference.
From now on, to log in to Passthrough, you will have to supply a password in addition to following a link from your email.