“Self Sovereign Identity” is a loosely defined term. Self-sovereign identity - Wikipedia
I’ve been studying it for a few years, and I’m not sure SSI alone really helps with @Emmo’s use case. SSI should afford for anyone to be empowered to present as the identity of their choice, perhaps amongst a bag of several identities that that same person uses in different contexts. groups of people, even, should perhaps be able to cooperate to present as a single identity… e.g. a software development team who cooperatively control a canister. For Tracking Prevention, the same device should also have a different Principal per canister. The Principal is not a unique identifier for the end-user.
If an end-user chooses to present themselves as many identities (or as part of a group identity), not just one, that’s a feature (to them), not a bug (maybe to you, but not to them). For example, I expect every human to have many Principals, at the very least because they will (probably) have a unique Principal for each device they use to access a given canister.
Now, this flexibility at the system layer may be frustrating to you ‘one ticket per person’ use case. On the other hand, there is nothing preventing someone from using this flexibility to build something less flexibile on top of it.
You should look into “Proof of Personhood”. It’s a hard problem. Definitely no ‘one size fits all’ approach that is ‘self-sovereign’ to the end-user and also ‘provably correct’ for someone with your use case, because by-my-understanding those two design goals are inherently at odds with one another.