We're recruiting participants by mail but don't want to use personal URLs because they are too long to type them in the cell phone.
My idea is to provide a three-digit alphanumeric code that participants would need to enter at the beginning of the questionnaire, which would allow us to identify them. How can I validate if the code provided by the user is from a list of codes? How would I set up Authenticator to do this? (if Authenticator is the appropriate tool).