You can use the "OTP" feature CROSStrax offers. This will require users to enter a code they receive via email in order to log in.
To active this feature go to the top of the page in CROSStrax>select the arrow next to your name>advanced settings>
Select add next to OTP>enable OTP>and choose how long to want the code to be valid for.
You will also need to make sure that the OTP is enabled for each user in their profile.