Custom variable in survey

Hi – I am trying to build a survey and the respondents will be able to remain anonymous so I wont have their email contact details. When they complete the survey, I need to present them with an onscreen UID that also sits with their survey data so that if I ever need to pull up their data, I can do so if they tell me their UID.

I know of some survey tools where I can do this with custome variables but not sure how to do this in wordpress or even if the functionality exists.

Am I better off just linking a third party survey tool into my wordpress site or can I do this in wordpress itself?

Many thanks to anyone who can assist.