"Migrations" tracking issue

[bitfl0wer]

Tracking issue for integration section #7 "Migrations" into the polyproto crate. This does not only involve implementation of routes, but the API design for the routes as well.

Identity migration

• Setting up a redirect
• Handle HTTP 307/308 status codes for routes, which request information about or send information to another actor, if this is needed

Re-signing messages

This might be a hard one. The protocol specification currently does not define a fixed schema for message re-signing batches.

• Handshake procedure
• Change ownership of messages signed by certain keys
• Change ownership of messages signed by all available keys
• Reduce amount of keys that need to be remembered
• "Rotate keys of past messages"

Moving data

• APIs for exporting data -> Protocol spec additions needed?
• APIs for importing data

Challenges and trust

• Verify challenge validity for challenges that involve migration -> Section 7.4 of the protocol