caBLE tunnel server

Cargo.toml

@@ -10,6 +10,10 @@ members = [
     "webauthn-rs",
     # Authenticator interactions
     "webauthn-authenticator-rs",
+    # caBLE tunnel server
+    "cable-tunnel-server/backend",
+    "cable-tunnel-server/common",
+    "cable-tunnel-server/frontend",
     "fido-key-manager",
     # Authenticator CLI,
     "authenticator-cli",
@@ -33,6 +37,7 @@ exclude = [
 
 [workspace.dependencies]
 base64urlsafedata = { path = "./base64urlsafedata" }
+cable-tunnel-server-common = { path = "./cable-tunnel-server/common" }
 webauthn-authenticator-rs = { path = "./webauthn-authenticator-rs" }
 webauthn-rs = { path = "./webauthn-rs" }
 webauthn-rs-core = { path = "./webauthn-rs-core" }
@@ -44,6 +49,10 @@ clap = { version = "^3.2", features = ["derive", "env"] }
 compact_jwt = "0.2.3"
 futures = "^0.3.25"
 hex = "0.4.3"
+http = "^0.2.9"
+http-body = "=1.0.0-rc.2"
+http-body-util = "=0.1.0-rc.2"
+hyper = { version = "=1.0.0-rc.3", default-features = false, features = ["http1"] }
 nom = "7.1"
 openssl = "^0.10.41"
 rand = "0.8"
@@ -53,8 +62,10 @@ serde_json = "^1.0.79"
 tide = "0.16"
 thiserror = "^1.0.37"
 tokio = { version = "1.22.0", features = ["sync", "test-util", "macros", "rt-multi-thread", "time"] }
+tokio-native-tls = "^0.3.1"
 tokio-tungstenite = { version = "^0.18.0", features = ["native-tls"] }
 tracing = "^0.1.35"
 tracing-subscriber = { version = "0.3", features = ["env-filter", "std", "fmt"] }
+tungstenite = { version = "^0.18.0", default-features = false, features = ["handshake"] }
 url = "2"
 uuid = "^1.1.2"

cable-tunnel-server/README.md

@@ -0,0 +1,113 @@
+# webauthn-rs caBLE tunnel server
+
+**Important:** it is only necessary for an *authenticator vendor* to run a caBLE
+tunnel service for their devices. Initiators (such as browsers and client
+applications) connect to a tunnel service of the *authenticator's* choosing.
+
+**Warning:** this is still a work in progress, and not yet fully implemented.
+
+However, you can run a single-task tunnel service with the `backend` alone:
+[see `./backend/README.md` for instructions][0].
+
+[0]: ./backend/README.md
+
+## Background
+
+To facilitate two-way communication between an initiator (browser) and
+authenticator (mobile phone), caBLE uses a WebSocket tunnel server. There are
+tunnel servers run by Apple (`cable.auth.com`) and Google (`cable.ua5v.com`),
+and a facility to procedurally generate new tunnel server domain names
+([run `webauthn-authenticator-rs`' `cable_domain` example][1]).
+
+[1]: ../webauthn-authenticator-rs/examples/cable_tunnel.rs
+
+As far as the tunnel server is concerned, what happens is:
+
+1. The authenticator and initator choose a 16 byte tunnel ID.
+
+2. The authenticator connects to a tunnel server of its choosing, using HTTPS.
+
+3. The authenticator makes a WebSocket request to `/cable/new/${TUNNEL_ID}`[^new].
+
+4. The tunnel server responds with a WebSocket handshake, and includes a 3 byte
+   routing ID in the HTTP response headers to indicate which task is serving
+   the request.
+
+5. The authenticator transmits the tunnel server ID and routing ID to the
+   initiator using an encrypted Bluetooth Low Energy advertisement.
+
+6. The initiator decrypts the advertisement, and connects to the tunnel server
+   using HTTPS.
+
+7. The initiator makes a WebSocket request to
+   `/cable/connect/${ROUTING_ID}/${TUNNEL_ID}`.
+
+8. The tunnel server responds with a WebSocket handshake.
+
+9. The tunnel server relays binary WebSocket messages between the authenticator
+   and initiator.
+
+The initiator starts a Noise channel with the authenticator for further
+communication such that the tunnel server cannot read their communications, and
+then does registration or authentication using the FIDO 2 protocol.
+
+Aside from implementing some basic request filtering, message limits and session
+limits, the tunnel server implementations are very simple. The tunnel server
+itself does not need to concern itself with the minutae of the Noise protocol -
+it only needs to pass binary messages across the tunnel verbatim.
+
+[^new]:
+  This [follows Google's caBLE URL convention][2]. The URL used to establish a
+  new channel [is not part of the FIDO 2.2 specification][3].
+
+[2]: https://source.chromium.org/chromium/chromium/src/+/main:device/fido/cable/v2_handshake.cc?q=symbol%3A%5Cbdevice%3A%3Acablev2%3A%3Atunnelserver%3A%3AGetNewTunnelURL%5Cb%20case%3Ayes
+[3]: https://fidoalliance.org/specs/fido-v2.2-rd-20230321/fido-client-to-authenticator-protocol-v2.2-rd-20230321.html#ref-for-client-platform①⓪
+
+## Design
+
+`webauthn-rs`' caBLE tunnel server consists of three parts:
+
+* [backend][]: serving binary which passes messages between the authenticator
+  and initiator on a known tunnel ID.
+
+* [frontend][]: serving binary which routes requests to a `backend` task based
+  on the routing ID (for `connect` / initiator requests), or some other load
+  balancing algorithm (for `new` / authenticator requests).
+
+* [common][]: contains all the shared web server, TLS and caBLE components for
+  the `backend` and `frontend` binaries.
+
+[backend]: ./backend/
+[frontend]: ./frontend/
+[common]: ./common/
+
+### Backend
+
+**Source:** [`./backend/`][backend]
+
+It should be possible to run the `backend` without a `frontend` – in this case
+the routing ID will be ignored, and all tunnels exist inside of a single serving
+task.
+
+### Frontend
+
+**Warning:** The `frontend` is not yet fully implemented, and does not yet do
+everything described here. This would be necessary to operate a
+high-availability caBLE tunnel service.
+
+**Source:** [`./frontend/`][frontend]
+
+The `frontend` needs to do some basic request processing (for routing) before
+handing off the connection to a `backend`:
+
+* For connecting to existing tunnels, the `frontend` needs to connect to
+  arbitrary `backend` tasks *in any location*.
+
+* For establishing new tunnels, the `frontend` should prefer to route to "local"
+  `backend` tasks, taking into account backend availability and load balancing.
+
+This will probably need some distributed lock service to allocate the routing
+IDs.
+
+While it would be possible to route based on the tunnel ID *alone*, this would
+make tunnel create / fetch operations (in the `backend`) global.

cable-tunnel-server/backend/Cargo.toml

@@ -0,0 +1,29 @@
+[package]
+name = "cable-tunnel-server-backend"
+version = "0.1.0"
+authors = ["Michael Farrell <[email protected]>"]
+categories = ["authentication"]
+description = "webauthn-rs caBLE tunnel server backend"
+edition = "2021"
+keywords = ["cable", "hybrid", "fido", "webauthn"]
+license = "MPL-2.0"
+readme = "README.md"
+repository = "https://github.com/kanidm/webauthn-rs/"
+rust-version = "1.66.0"
+
+[dependencies]
+cable-tunnel-server-common.workspace = true
+
+clap.workspace = true
+futures.workspace = true
+hex.workspace = true
+http-body.workspace = true
+http-body-util.workspace = true
+hyper = { workspace = true, features = ["server"] }
+thiserror.workspace = true
+tokio.workspace = true
+tokio-native-tls.workspace = true
+tokio-tungstenite.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true
+tungstenite.workspace = true

cable-tunnel-server/backend/README.md

@@ -0,0 +1,108 @@
+# webauthn-rs cable-tunnel-server-backend
+
+This binary provides a caBLE tunnel server, which is intended for
+*non-production use only*.
+
+The `backend` can run in two configurations:
+
+* a single-task configuration, directly serving requests with no frontend.
+
+  In this configuration, caBLE [Routing IDs][background] are ignored, and it is
+  presumed all incoming requests can be served out of a single running task.
+
+* a multi-task configuration, with many frontend tasks.
+
+  In this configuration, the backend presumes it has frontend tasks in front of
+  it to [handle caBLE Routing IDs][background]. However, the frontend is not yet
+  fully implemented.
+
+The `backend` is stateless, and is not capable of communicating with other
+tasks on its own. Each tunnel exists within one (*and only one*) `backend` task,
+and `backend` tasks never process caBLE [Routing IDs][background].
+
+[background]: ../README.md#background
+
+## Building
+
+You can build the `backend` using Cargo:
+
+```sh
+cargo build
+```
+
+This will output a binary to `./target/debug/cable-tunnel-server-backend`.
+
+You can also run the server via Cargo:
+
+```sh
+cargo run -- --help
+```
+
+## Configuring the server
+
+The server is configured with command-line flags, which can be seen by running
+the server with `--help`.
+
+To run the server at http://127.0.0.1:8080 (for testing with
+`webauthn-authenticator-rs` built with the `cable-override-tunnel` feature):
+
+```sh
+./cable-tunnel-server-backend \
+    --bind-address 127.0.0.1:8080 \
+    --insecure-http-server
+```
+
+To run the server with HTTPS and strict `Origin` header checks:
+
+```sh
+./cable-tunnel-server-backend \
+    --bind-address 192.0.2.1:443 \
+    --tls-public-key /etc/ssl/certs/cable.example.com.pem \
+    --tls-private-key /etc/ssl/certs/cable.example.com.key \
+    --origin cable.example.com
+```
+
+> **Important:** caBLE has an algorithm to deriving tunnel server domain names –
+> you cannot host the service on an arbitrary domain name of your choosing.
+>
+> Run [`webauthn-authenticator-rs`' `cable_domain` example][cable_domain] to
+> derive hostnames at the command line.
+
+[cable_domain]: ../../webauthn-authenticator-rs/examples/cable_domain.rs
+
+## Logging
+
+By default, the server runs at log level `info`. This can be changed with the
+`RUST_LOG` environment variable, using the
+[log levels available in the `tracing` crate][log-levels].
+
+The server logs the following at each level, plus all the messages in the levels
+above it:
+
+* `error`: TLS handshake errors, TCP connection errors, incorrect or unknown
+  HTTP requests
+
+* `warn`: warnings about using unencrypted HTTP
+
+* `info`: (default) start-up messages, HTTP connection lifetime, HTTP request
+  logs, WebSocket tunnel lifetime
+
+* `debug`: n/a
+
+* `trace`: adds complete incoming HTTP requests, WebSocket tunnel messages
+
+[log-levels]: https://docs.rs/tracing/*/tracing/struct.Level.html
+
+## Monitoring
+
+The server exports some basic metrics at `/debug`:
+
+* `server_state.strong_count`: the number of strong references to
+  `Arc<ServerState>`
+
+* `peer_map`: a `HashMap` of all pending tunnels - those where the authenticator
+  has connected but the initiator has not yet connected.
+
+  * `peer_map.capacity`: the capacity of the pending tunnels `HashMap`
+
+  * `peer_map.len`: the number of pending tunnels