SPIKE- Non-ephemeral connection to vc-authn agent

[esune]

In some circumstances, it would be great to be able to establish a non-ephemeral connection between the verifier agent and the mobile wallet: an example could be accessing a service where the user is automatically requested for the appropriate proof-request directly to their wallet, without presenting a QR code, if they have already visited the website and have established a connection with the verifier.

To fully support this, changes are required both at the verifier (vc-authn) layer and at the client application level using it for authentication. This issue would only cover the requirements and changes for vc-authn.

Initial brainstorming/concepts described here: https://hackmd.io/@esune/B1DFUwEoP.

[stale]

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