Feed Generator Service - DID Web Identity

[Ashex]

Service needs a DID Web for service auth

DID document structure

{
  "id": "did:web:<host>",
  "verificationMethod": [{
    "id": "did:web:<host>#atproto",
    "type": "Multikey",
    "controller": "did:web:<host>",
    "publicKeyMultibase": "<P-256 pubkey>"
  }],
  "service": [{
    "id": "#stratos_feedgen",
    "type": "NorthskyStratosFeedGen",
    "serviceEndpoint": "https://<host>"
  }]
}

To-do

• Generate P-256 signing keypair on initial start (or require generating it and document)
• Add stratos/stratos-feedgen/public/.well-known/did.json template

Acceptance criteria

• https://<host>/.well-known/did.json is publicly reachable and parses as a valid DID document
• idResolver.did.resolve('did:web:<host>') returns the published document from any external node
• Manual test: mint a service-auth JWT for the feed gen DID, call describeFeed via a PDS with atproto-proxy: did:web:<host>#stratos_feedgen — succeeds