alkssh/tests/auth_bridge.rs

//! The wave-2 auth-bridge contract tests (`w2-auth-bridge`): the
//! ADR-004 dispositions at the handler level and over the wire.
//!
//! Two vehicles, each for a structural reason:
//!
//! - **Wire rows** (the adapter's tokio-duplex mount + russh's own
//!   client, the `w2-server-mount` wire-smoke precedent) drive the full
//!   `auth_publickey` hook end to end (the hook's
//!   `VerifiedPublicKey`/`PublicKeyOffer` argument shapes are
//!   `#[non_exhaustive]` (only russh constructs them, post-verification),
//!   so wire traffic is the only way to observe the full hook, exactly
//!   where POC-1 observed it. These rows are the thin in-process
//!   precursor of the dedicated `w2-loopback-harness` vehicle (which
//!   records the transport choice and the helpers' vocabulary).
//! - **Direct-hook rows** (the wave-1 doubles against
//!   [`alkssh::SessionHandler`] constructed directly) drive every hook
//!   whose arguments are constructible outside russh: the four
//!   non-publickey declines, and the bridge core
//!   ([`alkssh::SessionHandler::resolve_bridge`], structured out of the
//!   `#[non_exhaustive]`-arg hook on purpose) with fixture keys +
//!   `MemIdentityProvider`. The non-constructible-arg hooks
//!   (`auth_publickey`, `auth_publickey_offered`) are the wire rows'
//!   business.
//!
//! The rows are contract stamps: each names the pinning ADR § (the
//! greppable `Contract stamp:` inventory applies).

mod common;

use std::sync::Arc;
use std::time::Duration;

use alkcall::core::auth::IdentityProvider;
use common::{FIXTURE_KEYS, MemHostKeySource, MemIdentityProvider, fixture, identity};
use russh::client::AuthResult;
use russh::keys::{Algorithm, Certificate, PrivateKeyWithHashAlg};
use russh::server::{Auth, Handler};

use alkssh::{AdapterError, Limits, ServeConfig, SessionHandler, SshAdapter, fingerprint};
use alkssh::{HostKeySource, KeySourceError};

/// The client-side handler double for the wire rows; it accepts every
/// host key (the test choice; the crate never embeds this posture).
struct AcceptAllHostKeys;

impl russh::client::Handler for AcceptAllHostKeys {
    type Error = russh::Error;

    async fn check_server_key(
        &mut self,
        _server_public_key: &russh::keys::PublicKeyOrCertificate,
    ) -> Result<bool, Self::Error> {
        Ok(true)
    }
}

/// Mounts the real adapter stack over an in-process duplex pair and
/// connects a russh client to it, the wire rows' vehicle.
async fn mount(
    provider: Arc<MemIdentityProvider>,
    limits: Limits,
) -> (
    russh::client::Handle<AcceptAllHostKeys>,
    tokio::task::JoinHandle<Result<(), AdapterError>>,
) {
    let mut serve_config = ServeConfig::new(
        Arc::clone(&provider) as Arc<dyn IdentityProvider>,
        Arc::new(MemHostKeySource::from_fixtures(&[fixture("bravo")])),
    );
    serve_config.limits = limits;

    let adapter = SshAdapter::new(serve_config)
        .await
        .expect("adapter constructs (host keys loaded)");
    let (client_io, server_io) = tokio::io::duplex(65_536);
    let server_task = tokio::spawn(async move { adapter.handle(server_io).await });

    let client_config = Arc::new(russh::client::Config {
        inactivity_timeout: Some(Duration::from_secs(30)),
        ..Default::default()
    });
    let client = russh::client::connect_stream(client_config, client_io, AcceptAllHostKeys)
        .await
        .expect("client mounts against the server stack");
    (client, server_task)
}

/// Ends one wire row cleanly: disconnect, then the server task's end.
async fn unmount(
    client: russh::client::Handle<AcceptAllHostKeys>,
    server_task: tokio::task::JoinHandle<Result<(), AdapterError>>,
) {
    client
        .disconnect(russh::Disconnect::ByApplication, "row done", "en")
        .await
        .expect("client disconnects cleanly");
    server_task
        .await
        .expect("server task ends")
        .expect("clean session end");
}

fn registered_provider(fingerprints: &[&str]) -> Arc<MemIdentityProvider> {
    let provider = Arc::new(MemIdentityProvider::new());
    for (index, registered) in fingerprints.iter().enumerate() {
        provider.register(registered, identity(&format!("user-{index}"), &["ssh"]));
    }
    provider
}

/// - *Contract stamp:* ADR-004 decision 1 (fingerprint →
///   `resolve_from_fingerprint` → `Some` → `Auth::Accept` (the bridge
///   accepts the identity's key with the arbitrary username attached).
#[tokio::test]
async fn known_fingerprint_accepts_over_the_wire() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);
    let (mut client, server_task) = mount(provider, Limits::default()).await;

    let result = client
        .authenticate_publickey(
            "anyone",
            PrivateKeyWithHashAlg::new(Arc::new(fixture("alpha").private_key()), None),
        )
        .await
        .expect("auth exchange completes over the wire");

    assert!(
        result.success(),
        "registered fingerprint must accept: {result:?}"
    );
    unmount(client, server_task).await;
}

/// - *Contract stamp:* ADR-004 decision 5 + OQ-03 (the username is not
///   identity and carries no semantics; keys resolve independently of
///   the username string, POC-1's `ssh anything@host` observation).
#[tokio::test]
async fn username_is_never_an_identity_input() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);

    for username in ["anyone", "git", "root", "alkforge"] {
        let (mut client, server_task) = mount(Arc::clone(&provider), Limits::default()).await;
        let result = client
            .authenticate_publickey(
                username,
                PrivateKeyWithHashAlg::new(Arc::new(fixture("alpha").private_key()), None),
            )
            .await
            .expect("auth exchange completes over the wire");
        assert!(
            result.success(),
            "every username authenticates identically: {username}: {result:?}"
        );
        unmount(client, server_task).await;
    }
}

/// - *Contract stamp:* ADR-004 decision 1 (`None` → reject; the
///   fail-closed path never creates a weakly authorized session) and
///   the advertisement honesty (ADR-004 decision 4, exactly
///   `{publickey}` remains advertised on the decline).
#[tokio::test]
async fn unknown_fingerprint_rejects_fail_closed() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);
    let (mut client, server_task) = mount(provider, Limits::default()).await;

    let result = client
        .authenticate_publickey(
            "anyone",
            PrivateKeyWithHashAlg::new(Arc::new(fixture("delta").private_key()), None),
        )
        .await
        .expect("auth exchange completes over the wire");

    let remaining = match &result {
        AuthResult::Failure {
            remaining_methods, ..
        } => remaining_methods.clone(),
        other => panic!("unregistered fingerprint must reject, got {other:?}"),
    };
    assert!(!result.success());
    assert_eq!(
        remaining,
        russh::MethodSet::from(&[russh::MethodKind::PublicKey][..]),
        "the publickey-only advertisement survives the decline"
    );
    unmount(client, server_task).await;
}

/// - *Contract stamp:* ADR-004 decision 1 (resolution happens at auth
///   time (a post-resolution revocation rejects the *next* attempt);
///   nothing is cached into a session credential).
#[tokio::test]
async fn resolved_fingerprint_can_be_revoked_between_attempts() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);
    let (mut client, server_task) = mount(Arc::clone(&provider), Limits::default()).await;

    let first = client
        .authenticate_publickey(
            "anyone",
            PrivateKeyWithHashAlg::new(Arc::new(fixture("alpha").private_key()), None),
        )
        .await
        .expect("auth exchange completes");
    assert!(first.success(), "registered fingerprint accepts: {first:?}");
    unmount(client, server_task).await;

    provider.revoke(fixture("alpha").fingerprint);

    let (mut client, server_task) = mount(provider, Limits::default()).await;
    let second = client
        .authenticate_publickey(
            "anyone",
            PrivateKeyWithHashAlg::new(Arc::new(fixture("alpha").private_key()), None),
        )
        .await
        .expect("auth exchange completes");
    assert!(!second.success(), "revoked fingerprint rejects: {second:?}");
    unmount(client, server_task).await;
}

/// - *Contract stamp:* ADR-004 decision 3 (`auth_none` is an explicit
///   family-contract decline; non-advertised methods are never
///   *advertised*, but the disposition is every attempted method's own
///   hook, not the advertisement's).
#[tokio::test]
async fn auth_none_rejects_over_the_wire() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);
    let (mut client, server_task) = mount(provider, Limits::default()).await;

    let result = client
        .authenticate_none("anyone")
        .await
        .expect("auth exchange completes over the wire");
    assert!(
        !result.success(),
        "the none method must never authenticate: {result:?}"
    );
    unmount(client, server_task).await;
}

/// - *Contract stamp:* ADR-004 decision 3 (`auth_password` explicit
///   decline; ADR-005's key custody is the whole client-side story).
#[tokio::test]
async fn auth_password_rejects_over_the_wire() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);
    let (mut client, server_task) = mount(provider, Limits::default()).await;

    let result = client
        .authenticate_password("anyone", "whatever")
        .await
        .expect("auth exchange completes over the wire");
    assert!(
        !result.success(),
        "the password method must never authenticate: {result:?}"
    );
    unmount(client, server_task).await;
}

/// - *Contract stamp:* ADR-004 decision 3 + OQ-04 (the OpenSSH
///   certificate decline is the standing disposition; no CA-trust
///   story exists in the family identity model).
#[tokio::test]
async fn auth_openssh_certificate_rejects_over_the_wire() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);
    let (mut client, server_task) = mount(provider, Limits::default()).await;

    let cert =
        Certificate::from_openssh(include_str!("vectors/alpha-cert.pub")).expect("cert fixture");
    let result = client
        .authenticate_openssh_cert("anyone", Arc::new(fixture("alpha").private_key()), cert)
        .await
        .expect("auth exchange completes over the wire");
    assert!(
        !result.success(),
        "an OpenSSH certificate must never authenticate: {result:?}"
    );
    unmount(client, server_task).await;
}

fn handler_with(provider: Arc<MemIdentityProvider>) -> SessionHandler {
    SessionHandler::new(Arc::new(ServeConfig::new(
        provider as Arc<dyn IdentityProvider>,
        Arc::new(MemHostKeySource::absent()),
    )))
}

/// - *Contract stamp:* ADR-004 decision 3 (each non-publickey method is
///   an *implemented* decline, never the inherited default; the
///   dispositions are family contract, and each one is its own hook).
#[tokio::test]
async fn every_non_publickey_hook_rejects_explicitly() {
    let mut handler = handler_with(registered_provider(&[fixture("alpha").fingerprint]));

    let none = handler.auth_none("anyone").await.expect("hook resolves");
    assert_eq!(none, Auth::reject(), "auth_none must decline");

    let password = handler
        .auth_password("anyone", "whatever")
        .await
        .expect("hook resolves");
    assert_eq!(password, Auth::reject(), "auth_password must decline");

    let keyboard = handler
        .auth_keyboard_interactive("anyone", "", None)
        .await
        .expect("hook resolves");
    assert_eq!(
        keyboard,
        Auth::reject(),
        "auth_keyboard_interactive must decline"
    );

    let cert = Certificate::from_openssh(include_str!("vectors/alpha-cert.pub"))
        .expect("cert fixture parses");
    let certificate = handler
        .auth_openssh_certificate("anyone", &cert)
        .await
        .expect("hook resolves");
    assert_eq!(
        certificate,
        Auth::reject(),
        "auth_openssh_certificate must decline"
    );

    assert!(
        handler.resolved_identity().is_none(),
        "no decline path may leave identity state behind"
    );
}

/// - *Contract stamp:* ADR-004 decision 1 (fingerprint →
///   `resolve_from_fingerprint` → `Some`, the single resolution shape,
///   with the crate's single fingerprint path computing the handle the
///   doubles registered).
#[tokio::test]
async fn bridge_core_resolves_registered_fingerprints() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);
    let handler = handler_with(provider);
    let key = fixture("alpha").public_key();

    let resolved = handler
        .resolve_bridge(&key, &Algorithm::Ed25519)
        .expect("registered fingerprint resolves");
    assert_eq!(resolved.id, "user-0", "the identity rides to the handler");
    assert!(
        handler.resolved_identity().is_none(),
        "resolve_bridge only resolves (the hook stores; an unwired bridge leaves no state)"
    );
}

/// - *Contract stamp:* ADR-004 decision 1 (`None` → reject; the
///   unknown / revoked fingerprint never resolves; fail-closed, no
///   weakly-authorized session, no cached resolution).
#[tokio::test]
async fn bridge_core_rejects_unknown_and_revoked_fingerprints() {
    let provider = Arc::new(MemIdentityProvider::new());
    let handler = handler_with(Arc::clone(&provider));
    let key = fixture("delta").public_key();

    assert!(
        handler.resolve_bridge(&key, &Algorithm::Ed25519).is_none(),
        "an unregistered fingerprint resolves to the reject disposition"
    );

    provider.register(
        fixture("delta").fingerprint,
        identity("user-delta", &["ssh"]),
    );
    assert!(
        handler.resolve_bridge(&key, &Algorithm::Ed25519).is_some(),
        "the registration lands"
    );

    provider.revoke(fixture("delta").fingerprint);
    assert!(
        handler.resolve_bridge(&key, &Algorithm::Ed25519).is_none(),
        "the revocation takes; no cached resolution survives"
    );
}

/// - *Contract stamp:* ADR-002 decision 4 (ed25519-only: the
///   non-ed25519 decline is explicit-over-inherited and precedes any
///   resolution: a registered fingerprint under a non-ed25519
///   algorithm still declines). The sk-variant and `Other` stand-ins
///   cover the scheme classes the in-tree build cannot even parse
///   (rsa/dsa are dropped from the dependency tree and ssh-key ships
///   without ecdsa/dsa/rsa features here, so no wire row can drive a
///   non-ed25519 key at this pin (recorded in the task notes); the
///   gate is the explicit-over-inherited posture for the bump).
#[tokio::test]
async fn bridge_core_gates_non_ed25519_algorithms_before_resolution() {
    let provider = registered_provider(&[fixture("alpha").fingerprint]);
    let handler = handler_with(provider);
    let key = fixture("alpha").public_key();

    assert_eq!(key.algorithm(), Algorithm::Ed25519);
    for non_ed25519 in [
        Algorithm::SkEd25519,
        Algorithm::SkEcdsaSha2NistP256,
        Algorithm::Other(
            "rsa-class@alkssh.gate-vector"
                .parse()
                .expect("algorithm name parses"),
        ),
    ] {
        let resolved = handler.resolve_bridge(&key, &non_ed25519);
        assert!(
            resolved.is_none(),
            "the ed25519-only gate precedes resolution: {non_ed25519:?}"
        );
    }

    assert!(
        handler.resolve_bridge(&key, &Algorithm::Ed25519).is_some(),
        "the same registered fingerprint resolves under the ed25519 algorithm"
    );
}

/// - *Contract stamp:* ADR-004 decision 1 (the fingerprint the bridge
///   computes is byte-format identical to the independent-issuer
///   registrations; the wave-1 parity vectors pin the string, and this row
///   pins that the bridge resolves against exactly those values).
#[tokio::test]
async fn bridge_core_fingerprint_is_the_registered_value() {
    let provider = Arc::new(MemIdentityProvider::new());
    provider.register(
        fixture("bravo").fingerprint,
        identity("user-bravo", &["ssh"]),
    );
    let handler = handler_with(provider);

    let resolved = handler
        .resolve_bridge(&fixture("bravo").public_key(), &Algorithm::Ed25519)
        .expect("independent-issuer registration value resolves");
    assert_eq!(resolved.id, "user-bravo");
}

/// - *Contract stamp:* ADR-004 decision 1 (`SHA256:` + unpadded
///   standard-alphabet base64 (the wave-1 record), re-asserted against
///   every committed fixture's `ssh-keygen -lf` value).
#[test]
fn every_fixture_fingerprint_format_stays_the_contract_invariant_shape() {
    for fixture_key in FIXTURE_KEYS {
        let computed = fingerprint(&fixture_key.public_key());
        assert_eq!(
            computed, fixture_key.fingerprint,
            "fixture {} must keep its recorded ssh-keygen value",
            fixture_key.name
        );
    }
}

/// - *Contract stamp:* ADR-005 decision 6 (host-key loading is the
///   construction's business, never the auth hooks'; the bridge
///   handler builds over an absent host-key source and never loads it,
///   and the absent shape still refuses fail-closed if it were).
#[tokio::test]
async fn handler_constructs_over_an_absent_host_key_source_without_loading_it() {
    let provider = registered_provider(&[]);
    let serve_config = ServeConfig::new(
        provider as Arc<dyn IdentityProvider>,
        Arc::new(MemHostKeySource::absent()),
    );
    let handler = SessionHandler::new(Arc::new(serve_config));

    assert!(handler.resolved_identity().is_none(), "no auth yet");

    let err = MemHostKeySource::absent()
        .load()
        .await
        .expect_err("the absent shape refuses");
    assert!(matches!(err, KeySourceError::Absent));
}