src-tauri/src/mcp/token.rs

@@ -0,0 +1,90 @@
+//! MCP auth-token storage (FR-MCP-1/6). The token itself is **never** written
+//! to `settings.json`/`wa.db`/logs — only the OS credential store, exactly
+//! like sync secrets (`sync::credentials`) and hosted-AI API keys.
+
+use crate::mcp::McpError;
+
+const SERVICE: &str = "WhispAssist-mcp";
+const ACCOUNT: &str = "token";
+const TOKEN_BYTES: usize = 32;
+
+fn entry() -> Result<keyring::Entry, McpError> {
+    keyring::Entry::new(SERVICE, ACCOUNT).map_err(|e| McpError::Server(e.to_string()))
+}
+
+/// Generates a fresh random token (hex-encoded, 64 chars) and persists it,
+/// replacing whatever was there before (each `set_mcp_enabled` mints a new
+/// one — there is no "reveal the existing token" path, same treatment as a
+/// password).
+pub fn mint_and_store() -> Result<String, McpError> {
+    let mut buf = [0u8; TOKEN_BYTES];
+    getrandom::getrandom(&mut buf).map_err(|e| McpError::Server(e.to_string()))?;
+    let token = hex_encode(&buf);
+    entry()?
+        .set_password(&token)
+        .map_err(|e| McpError::Server(e.to_string()))?;
+    Ok(token)
+}
+
+/// Best-effort read for `mcp_status`'s `tokenSet` flag — never returned to
+/// the frontend as a value, only whether one exists.
+pub fn is_set() -> bool {
+    entry().and_then(|e| e.get_password().map_err(|e| McpError::Server(e.to_string()))).is_ok()
+}
+
+pub fn get() -> Result<String, McpError> {
+    entry()?
+        .get_password()
+        .map_err(|e| McpError::Server(e.to_string()))
+}
+
+/// Best-effort cleanup on disable — a missing entry is not an error.
+pub fn delete() {
+    if let Ok(e) = entry() {
+        match e.delete_credential() {
+            Ok(()) | Err(keyring::Error::NoEntry) => {}
+            Err(err) => tracing::warn!("failed to delete MCP token: {err}"),
+        }
+    }
+}
+
+/// Constant-time comparison so token checking doesn't leak timing
+/// information about how many leading bytes matched (NFR-SEC-5).
+pub fn verify(presented: &str, expected: &str) -> bool {
+    let a = presented.as_bytes();
+    let b = expected.as_bytes();
+    if a.len() != b.len() {
+        return false;
+    }
+    let mut diff = 0u8;
+    for (x, y) in a.iter().zip(b.iter()) {
+        diff |= x ^ y;
+    }
+    diff == 0
+}
+
+fn hex_encode(bytes: &[u8]) -> String {
+    let mut s = String::with_capacity(bytes.len() * 2);
+    for b in bytes {
+        s.push_str(&format!("{b:02x}"));
+    }
+    s
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn verify_requires_exact_match() {
+        assert!(verify("abc123", "abc123"));
+        assert!(!verify("abc123", "abc124"));
+        assert!(!verify("abc12", "abc123"));
+        assert!(!verify("", "abc123"));
+    }
+
+    #[test]
+    fn hex_encode_is_lowercase_and_fixed_width() {
+        assert_eq!(hex_encode(&[0, 255, 16]), "00ff10");
+    }
+}