feat: secure_session commands, login tokens in the OS keychain (cinny #105, step 1)

Commands for the web client to keep a copy of the login tokens in the OS
keychain: secure_session_supported / _set / _get / _clear.

- Windows: Credential Manager via the keyring crate (3.6, windows-native),
  entry "session" in service "Lotus Chat". Only the secrets are stored
  (userId, deviceId, accessToken, refreshToken); the serialized value is
  capped at 1200 chars (Windows' limit is 2560 bytes).
- Other platforms: supported = false and the other commands answer "not
  supported on this platform" (Linux Secret Service can prompt to unlock a
  wallet at startup; that needs its own testing). No new Linux dependency:
  without a platform feature the crate only has its mock store.
- Keychain calls run on the blocking pool, off the main thread.

Step 1 is a mirror only (the web client still reads its session from
localStorage); see the cinny PR.

Tests: round trip + clear, clearing an empty keychain, incomplete and
oversized sessions rejected with nothing written, the JSON shape the web
client sends, a realistic OIDC session fits (keyring's mock store). Linux
release build: commands answer as designed and login is unaffected.
Windows: type-checked only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src-tauri/Cargo.lock

@@ -498,6 +498,7 @@ checksum = "6e4de3bc4ea267985becf712dc6d9eed8b04c953b3fcfb339ebc87acd9804901"
 name = "cinny"
 version = "4.12.2"
 dependencies = [
+ "keyring",
  "serde",
  "serde_json",
  "tauri",
@@ -2090,6 +2091,18 @@ dependencies = [
  "unicode-segmentation",
 ]
 
+[[package]]
+name = "keyring"
+version = "3.6.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eebcc3aff044e5944a8fbaf69eb277d11986064cba30c468730e8b9909fb551c"
+dependencies = [
+ "byteorder",
+ "log",
+ "windows-sys 0.60.2",
+ "zeroize",
+]
+
 [[package]]
 name = "kuchikiki"
 version = "0.8.8-speedreader"

src-tauri/Cargo.toml

@@ -38,6 +38,10 @@ tauri-plugin-single-instance = "2"
 tauri-plugin-autostart = "2" # P6-1 launch-on-login
 # Update retry backoff (already in the tree via tauri; adds only the timer).
 tokio = { version = "1", features = ["time"] }
+# cinny #105: login tokens in the OS keychain. Without a platform feature
+# the crate only has its in-memory mock store (used by the tests); Windows
+# turns on Credential Manager below.
+keyring = "3.6"
 
 [target.'cfg(target_os = "linux")'.dependencies]
 # P6-1 desktop parity: screensaver inhibit (no-sleep in calls) + Unity launcher
@@ -50,6 +54,7 @@ zbus = "5"
 webkit2gtk = "2.0"
 
 [target.'cfg(target_os = "windows")'.dependencies]
+keyring = { version = "3.6", features = ["windows-native"] }
 webview2-com = "0.38"
 window-vibrancy = "0.6"
 windows = { version = "0.61", features = [

src-tauri/src/lib.rs

@@ -13,6 +13,7 @@ use tauri_plugin_opener::OpenerExt;
 
 pub mod gpu_workarounds;
 mod native;
+mod secure_session;
 
 /// Bring the main window to the foreground from the tray / a hidden /
 /// minimized state. Shared by the tray, single-instance, and deep-link paths.
@@ -952,6 +953,10 @@ pub fn run() {
             native::focus_assist::get_focus_assist,
             native::hotkeys::global_hotkeys_supported,
             native::hotkeys::set_global_hotkeys,
+            secure_session::secure_session_supported,
+            secure_session::secure_session_set,
+            secure_session::secure_session_get,
+            secure_session::secure_session_clear,
         ])
         .plugin(tauri_plugin_localhost::Builder::new(port).build())
         .plugin(

src-tauri/src/secure_session.rs

@@ -0,0 +1,181 @@
+//! Login tokens in the OS keychain (cinny #105, step 1).
+//!
+//! Step 1 only MIRRORS the session tokens into the keychain (Windows
+//! Credential Manager): the web client keeps reading its session from
+//! localStorage exactly as before, so nothing about login changes and a
+//! keychain problem can't log anyone out. Once the mirror has proven itself on
+//! real installs, step 2 switches reads to the keychain and drops the tokens
+//! from localStorage.
+//!
+//! Only the secrets are stored (user id + device id to match them to the
+//! session, the access token and the refresh token); the rest of the session
+//! stays in localStorage. Windows caps a credential at 2560 bytes, so the
+//! serialized value is limited well below that.
+//!
+//! Other platforms: not supported yet (Linux Secret Service can prompt to
+//! unlock a wallet at startup; that needs its own testing), and the commands
+//! say so instead of failing.
+
+use serde::{Deserialize, Serialize};
+
+#[cfg_attr(not(any(target_os = "windows", test)), allow(dead_code))]
+pub(crate) const SERVICE: &str = "Lotus Chat";
+#[cfg_attr(not(any(target_os = "windows", test)), allow(dead_code))]
+pub(crate) const ACCOUNT: &str = "session";
+/// Serialized-length cap (chars). Windows' limit is 2560 bytes; staying under
+/// 1200 chars keeps us safe whether the value is stored as UTF-8 or UTF-16.
+pub(crate) const MAX_LEN: usize = 1200;
+
+#[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq)]
+#[serde(rename_all = "camelCase")]
+pub struct SessionTokens {
+    pub user_id: String,
+    pub device_id: String,
+    pub access_token: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub refresh_token: Option<String>,
+}
+
+pub(crate) fn store(entry: &keyring::Entry, tokens: &SessionTokens) -> Result<(), String> {
+    if tokens.user_id.is_empty() || tokens.device_id.is_empty() || tokens.access_token.is_empty() {
+        return Err("incomplete session".into());
+    }
+    let value = serde_json::to_string(tokens).map_err(|e| e.to_string())?;
+    if value.chars().count() > MAX_LEN {
+        return Err(format!(
+            "session too large for the keychain ({} chars)",
+            value.chars().count()
+        ));
+    }
+    entry.set_password(&value).map_err(|e| e.to_string())
+}
+
+pub(crate) fn load(entry: &keyring::Entry) -> Result<Option<SessionTokens>, String> {
+    match entry.get_password() {
+        Ok(value) => serde_json::from_str(&value)
+            .map(Some)
+            .map_err(|e| format!("unreadable keychain entry: {e}")),
+        Err(keyring::Error::NoEntry) => Ok(None),
+        Err(e) => Err(e.to_string()),
+    }
+}
+
+pub(crate) fn clear(entry: &keyring::Entry) -> Result<(), String> {
+    match entry.delete_credential() {
+        Ok(()) | Err(keyring::Error::NoEntry) => Ok(()),
+        Err(e) => Err(e.to_string()),
+    }
+}
+
+#[cfg(target_os = "windows")]
+fn entry() -> Result<keyring::Entry, String> {
+    keyring::Entry::new(SERVICE, ACCOUNT).map_err(|e| e.to_string())
+}
+
+#[cfg(not(target_os = "windows"))]
+fn entry() -> Result<keyring::Entry, String> {
+    Err("not supported on this platform".into())
+}
+
+/// Keychain calls can block (credential store, AV scanners): keep them off
+/// the main thread.
+async fn blocking<T: Send + 'static>(
+    f: impl FnOnce() -> Result<T, String> + Send + 'static,
+) -> Result<T, String> {
+    tauri::async_runtime::spawn_blocking(f)
+        .await
+        .map_err(|e| e.to_string())?
+}
+
+/// Whether this platform stores the session in the keychain.
+#[tauri::command]
+pub fn secure_session_supported() -> bool {
+    cfg!(target_os = "windows")
+}
+
+#[tauri::command]
+pub async fn secure_session_set(tokens: SessionTokens) -> Result<(), String> {
+    blocking(move || store(&entry()?, &tokens)).await
+}
+
+#[tauri::command]
+pub async fn secure_session_get() -> Result<Option<SessionTokens>, String> {
+    blocking(|| load(&entry()?)).await
+}
+
+#[tauri::command]
+pub async fn secure_session_clear() -> Result<(), String> {
+    blocking(|| clear(&entry()?)).await
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn mock_entry() -> keyring::Entry {
+        keyring::set_default_credential_builder(keyring::mock::default_credential_builder());
+        keyring::Entry::new(SERVICE, ACCOUNT).unwrap()
+    }
+
+    fn tokens() -> SessionTokens {
+        SessionTokens {
+            user_id: "@alice:lotusguild.org".into(),
+            device_id: "ABCDEFGHIJ".into(),
+            access_token: "syt_YWxpY2U_abcdefghijklmnopqrst_0AbCdE".into(),
+            refresh_token: None,
+        }
+    }
+
+    #[test]
+    fn round_trip_and_clear() {
+        let e = mock_entry();
+        assert_eq!(load(&e).unwrap(), None);
+        store(&e, &tokens()).unwrap();
+        assert_eq!(load(&e).unwrap(), Some(tokens()));
+        let mut oidc = tokens();
+        oidc.refresh_token = Some("mar_refresh_token_value_0123456789".into());
+        store(&e, &oidc).unwrap();
+        assert_eq!(load(&e).unwrap(), Some(oidc));
+        clear(&e).unwrap();
+        assert_eq!(load(&e).unwrap(), None);
+        // Clearing an empty keychain is fine (logout twice, or never mirrored).
+        clear(&e).unwrap();
+    }
+
+    #[test]
+    fn rejects_incomplete_or_oversized_sessions() {
+        let e = mock_entry();
+        let mut t = tokens();
+        t.access_token = String::new();
+        assert!(store(&e, &t).is_err());
+        let mut big = tokens();
+        big.access_token = "x".repeat(MAX_LEN);
+        assert!(store(&e, &big).unwrap_err().contains("too large"));
+        assert_eq!(load(&e).unwrap(), None, "nothing written on error");
+    }
+
+    #[test]
+    fn serialized_shape_matches_the_web_client() {
+        let json = serde_json::to_value(tokens()).unwrap();
+        assert_eq!(json["userId"], "@alice:lotusguild.org");
+        assert_eq!(json["deviceId"], "ABCDEFGHIJ");
+        assert!(json.get("refreshToken").is_none());
+        let back: SessionTokens = serde_json::from_str(
+            r#"{"userId":"@a:b","deviceId":"D","accessToken":"t","refreshToken":"r"}"#,
+        )
+        .unwrap();
+        assert_eq!(back.refresh_token.as_deref(), Some("r"));
+    }
+
+    #[test]
+    fn a_realistic_oidc_session_fits() {
+        let e = mock_entry();
+        let t = SessionTokens {
+            user_id: format!("@{}:matrix.lotusguild.org", "a".repeat(60)),
+            device_id: "X".repeat(40),
+            access_token: "mat_".to_string() + &"A".repeat(200),
+            refresh_token: Some("mar_".to_string() + &"B".repeat(200)),
+        };
+        store(&e, &t).unwrap();
+    }
+}