# Park Passport

Mobile-first PWA for GPS-verified National Park stamps. Identity and data live on AT Protocol. This is a Rust rewrite of the original Go implementation (`~/cairns`).

## Stack

| Layer       | Technology                      |
|-------------|---------------------------------|
| Frontend    | Vanilla JS PWA (React Native later) |
| Backend     | Rust (axum), hosted on Fly.io   |
| Identity    | AT Protocol / Bluesky OAuth     |
| User data   | User's own AT Protocol PDS      |
| Park data   | NPS Public API + bundled GeoJSON |
| Credentials | W3C Verifiable Credentials 2.0  |

## Architecture

The backend issues signed W3C VCs but stores nothing. All stamp records and VC blobs live on the user's PDS.

```
Client                    Verification Service           User PDS
  │                               │                          │
  ├─ { did, parkId, coords } ────►│                          │
  │                               ├─ check GeoJSON boundary  │
  │                               ├─ sign VC (EdDSA)         │
  │                               ├─ write VC blob ─────────►│
  │◄─ vcRef (CID) ────────────────│                          │
  │                                                          │
  ├─ write app.parkpassport.stamp record ───────────────────►│
```

## Stamp Record (`app.parkpassport.stamp`)

```
parkId              string
visitedAt           datetime
verificationMethod  "gps"
vcRef               blob ref (CID of VC blob in PDS blob store)
```

## Verifiable Credential Structure

```json
{
  "@context": ["https://www.w3.org/ns/credentials/v2"],
  "type": ["VerifiableCredential", "NationalParkStamp"],
  "issuer": "did:web:verify.parkpassport.app",
  "validFrom": "2026-03-22T14:30:00Z",
  "credentialSubject": {
    "id": "did:plc:abc123",
    "parkId": "acadia",
    "parkName": "Acadia National Park",
    "visitedAt": "2026-03-22T14:30:00Z",
    "verificationMethod": "gps"
  },
  "proof": {
    "type": "DataIntegrityProof",
    "cryptosuite": "eddsa-rdfc-2022",
    "verificationMethod": "did:web:verify.parkpassport.app#key-1",
    "proofValue": "..."
  }
}
```

Stamps are independently verifiable: fetch the VC blob from the user's PDS, fetch the issuer public key from `https://verify.parkpassport.app/.well-known/did.json`, verify the EdDSA signature.

## Key Endpoints

| Endpoint                    | Purpose                                         |
|-----------------------------|-------------------------------------------------|
| `POST /api/stamp`           | Issue a signed VC for a GPS-verified park visit |
| `GET /api/stamps`           | Fetch user's stamps from their PDS              |
| `GET /api/me`               | Return `{ did, handle }` for auth state         |
| `GET /auth/login`           | Start Bluesky OAuth flow                        |
| `GET /auth/callback`        | Complete OAuth, set session cookie              |
| `GET /.well-known/did.json` | Issuer DID document with public key             |

## Key Crates

| Purpose       | Crate              |
|---------------|--------------------|
| HTTP server   | `axum`             |
| HTTP client   | `reqwest`          |
| Async runtime | `tokio`            |
| DNS           | `hickory-resolver` |
| JSON          | `serde`, `serde_json` |
| Error handling | `anyhow`          |
| Cookies       | `tower-cookies`    |
| Geo           | `geo`              |
| Ed25519       | `ed25519-dalek`    |

## Infrastructure

- Issuer DID: `did:web:verify.parkpassport.app`
- Public key: `https://verify.parkpassport.app/.well-known/did.json`
- User data: user's existing Bluesky PDS (no database)
- Deploy: `fly deploy`