Add option of including context information in construction of UN

[jot2re]

Currently a UN can be used multiple times within its validity.
This is a feature that allows it to be used repeatedly in short sessions without needing the user to sign a new UN.
However, this can also be a security risk in some contexts.
This task is about allowing an optional extra parameter to be used in the cryptographic process of constructing a UN, which can be used to link the UN to a specific context, which can also locally be verified by a verifier.

[SmartLayer]

Unclear. Do you mean the UN should contain the hash of the current website domain or URL?

[jot2re]

This is more a "nice to have".
I talked with @oleggrib about this, and currently a UN can be reused during its entire validity. We discussed that this is generally not the functionality we actually want. We generally want it to just work a single time. However, this does not seem to currently be a big security issue.

[jot2re]

Yes, it is a nice "hack" of how to do it. Because basically it is all a question of optionally adding an extra parameter which gets hashed, but since the domain is already getting hashed, this can be done implicitly through the domain string.
But it is a bit more pretty and easier to read/understand using parametrisation.