Postal access code verification for anonymous survey responses

Is your feature request related to a problem? Please describe.
The current verification methods are quite labor intensive, either for participants or for administrators. They usually achieve a level of verification valid for longer periods of time and intended for uses in multiple processes. They are not really useful for scoping smaller sample sizes (e.g. verifying that you are from a certain neighbourhood, street or any other smaller target group). Lastly, they may require data not available (i.e. email addresses).

Describe the solution you'd like
We would like to develop a solution where project manages can determine a sample size of participants (e.g. inhabitants in a street) and create a limited amount of acceses to a component. These links could then be sent by post as a QR-code and automatically allow participation for that session.

As a participant I would recieve a letter, open the QR-code and automatically be directed to the survey, which I would be able to fill out. Access to the survey is only granted when coming from a code, which would be valid until the survey is submitted. This allows for starting the survey multiple times (i.e. when I switch devices), but only submitting survey responses once per code.

In a first phase, we would develop this for the survey component, as it allows non-registered participation. Additionally, we would primarily focus on codes that could be used once. A setting allowing X-amounts of uses per code could be developed in later phase.

Describe alternatives you've considered
So far, we have considered:

• Using private processes: we do not know the email addresses of the users at the beginning of the process, so we can't invite them. Additionaly, we want anonymous participation to be possible
• standard verifications: do not work as mentioned in the problem statement
• Decidim Access codes: Does not work because we do not know the email addresses

Additional context
We must consider dependencies when starting development on ephemeral user registration according to the roadmap (https://github.com/orgs/decidim/projects/22?pane=issue&itemId=34383439).

Does this issue could impact on users private data?
Additional user data (i.e. postal adresses) would not be handled on decidim. Decidim just handles the codes, so there is no impact on user data. Any additional data would be covered in the terms of the survey component.

Funded by
City of Zürich, development probably in the Q1 2024