Two-Factor Authentication can now be done by SMS, thanks to a third-party third-party cloud platform, Twilio. You will just have to create a free account on their website and enter the corresponding account information on the Configure SMS tab of the Two-Factor Authentication Add-On.
Two-factor authentication is available with HTML5 and Remoteapp connections on TSplus Web portal only, on TSplus Mobile Web and Enterprise Editions. This authentication mode does not support login through Remote Desktop client. For more information, check this documentation.