add passkey support

README.md

@@ -8,7 +8,13 @@ A small shared grocery list built with Rust, Axum, Maud, htmx, WebSockets, and S
 cargo run
 ```
 
-Open <http://127.0.0.1:3000>. The application creates `sustenance.db` in the working directory on first start.
+Open <http://localhost:3000>. The application creates `sustenance.db` in the
+working directory on first start.
+
+**Note:** use `localhost` (not `127.0.0.1`) when testing passkeys locally —
+browsers reject IP addresses as WebAuthn RP IDs. The app defaults to
+`localhost` for loopback hosts, so passkeys work out of the box when you access
+the site via `http://localhost:3000`.
 
 ## Configuration
 
@@ -20,6 +26,8 @@ Open <http://127.0.0.1:3000>. The application creates `sustenance.db` in the wor
 | `COOKIE_SECURE` | `false` | Add the `Secure` attribute to session cookies |
 | `REGISTRATION_MODE` | `invite_only` | Use `open` for local development; otherwise registration requires a valid list invitation after the first account |
 | `SEED_CONFIG` | `seed.json` | Optional JSON file with a default user to create when the database is first initialized |
+| `RP_ID` | derived from `PUBLIC_BASE_URL` | WebAuthn relying party ID (the host users access the site from) |
+| `RP_NAME` | `Sustenance` | WebAuthn relying party name shown to users |
 | `RUST_LOG` | `sustenance=info,tower_http=info` | Log filter; HTTP requests are logged at info level |
 
 ### Seeding a default user
@@ -41,6 +49,7 @@ The file is optional — if it is missing or invalid, seeding is silently skippe
 ## Current features
 
 - Email/password accounts with Argon2 password hashes
+- Optional WebAuthn passkeys for passwordless sign-in (managed from the account page)
 - Cookie-backed sessions and CSRF tokens for list mutations
 - Shared lists with one-time, seven-day invitation links
 - Invite-only registration by default after the first account