GDPR-friendly and agnostic conversion tracking

[eric-burel]

Goal:

• get number of visits
• get an approximation of unique visitors

Constraints:

• avoid personal data so no IP
• avoid JS cookies (see Safari ITP https://www.apple.com/safari/docs/Safari_White_Paper_Nov_2019.pdf) so favour HTTP-only cookies
• assign a token to new visitors if they don't have one (can be done in middleware I think, though setting cookies used to have some bugs in earlier versions)
• associate token and userId upon connexion, in particular for magic login with email

Tech choices:

• there might be existing solutions for Next we don't need to reinvent the wheel
• store data on Mongo? Is it ok to have a lot of queries? Redis is better suited for fast computation but it doesn't preserve values, so we have to regularly store new data anyway. Perhaps useful for optimization
• we'll need a few queries to compute the counts from raw events
• • UI in surveyadmin

@SachaG

[eric-burel]

Plausible could be self-hosted: https://plausible.io/data-policy It seems to use a hashed IP address with rotating salt, which could be ok in our use case (as long as the IP can't be retrieved later on)

[SachaG]

I'm already paying for the non-self-hosted Plausible so we could always just use that if we don't want to build our own internal tracking system.

[eric-burel]

I've read the Plausible doc and it's 100% what we need Vercel is not bad either, and included anyway so we can't stick to it for non self-hosted surveys