feat: add license validation and entitlements (Rust) (#46)

Introduces the offline license infrastructure for the Base/Premium editions.

- jsonwebtoken (EdDSA) verifies license JWTs against an embedded Ed25519
  public key. The exp claim is mandatory (CWE-613) and is enforced via
  Validation::set_required_spec_claims.
- Activation tokens (server-issued, machine-bound) prevent license.key
  copying between machines. Storage is wired up; the actual issuance flow
  ships with Issue #49.
- get_edition() fails closed to "free" when the license is missing,
  invalid, expired, or activated for a different machine.
- New commands/entitlements module centralizes feature → tier mapping so
  Issue #48 (and any future gate) reads from a single source of truth.
- machine-uid provides the cross-platform machine identifier; OS reinstall
  invalidates the activation token by design.
- Tests cover happy path, expiry, wrong-key signature, malformed JWT,
  unknown edition, and machine_id matching for activation tokens.

The embedded PUBLIC_KEY_PEM is the RFC 8410 §10.3 test vector, clearly
labelled as a development placeholder; replacing it with the production
public key is a release-time task.

src-tauri/Cargo.toml

@@ -35,4 +35,8 @@ walkdir = "2"
 aes-gcm = "0.10"
 argon2 = "0.5"
 rand = "0.8"
+jsonwebtoken = "9"
+machine-uid = "0.5"
 
+[dev-dependencies]
+ed25519-dalek = { version = "2", features = ["pkcs8", "pem", "rand_core"] }

src-tauri/src/commands/entitlements.rs

@@ -0,0 +1,67 @@
+// Centralized feature → tier mapping for license entitlements.
+//
+// This module is the single source of truth for which features are gated by which tier.
+// To change what is gated where, modify FEATURE_TIERS only — never sprinkle edition checks
+// throughout the codebase.
+
+/// Editions, ordered from least to most privileged.
+pub const EDITION_FREE: &str = "free";
+pub const EDITION_BASE: &str = "base";
+pub const EDITION_PREMIUM: &str = "premium";
+
+/// Maps feature name → list of editions allowed to use it.
+/// A feature absent from this list is denied for all editions.
+const FEATURE_TIERS: &[(&str, &[&str])] = &[
+    ("auto-update", &[EDITION_BASE, EDITION_PREMIUM]),
+    ("web-sync", &[EDITION_PREMIUM]),
+    ("cloud-backup", &[EDITION_PREMIUM]),
+    ("advanced-reports", &[EDITION_PREMIUM]),
+];
+
+/// Pure check: does `edition` grant access to `feature`?
+pub fn is_feature_allowed(feature: &str, edition: &str) -> bool {
+    FEATURE_TIERS
+        .iter()
+        .find(|(name, _)| *name == feature)
+        .map(|(_, tiers)| tiers.contains(&edition))
+        .unwrap_or(false)
+}
+
+#[tauri::command]
+pub fn check_entitlement(app: tauri::AppHandle, feature: String) -> Result<bool, String> {
+    let edition = crate::commands::license_commands::current_edition(&app);
+    Ok(is_feature_allowed(&feature, &edition))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn free_blocks_auto_update() {
+        assert!(!is_feature_allowed("auto-update", EDITION_FREE));
+    }
+
+    #[test]
+    fn base_unlocks_auto_update() {
+        assert!(is_feature_allowed("auto-update", EDITION_BASE));
+    }
+
+    #[test]
+    fn premium_unlocks_everything() {
+        assert!(is_feature_allowed("auto-update", EDITION_PREMIUM));
+        assert!(is_feature_allowed("web-sync", EDITION_PREMIUM));
+        assert!(is_feature_allowed("cloud-backup", EDITION_PREMIUM));
+    }
+
+    #[test]
+    fn base_does_not_unlock_premium_features() {
+        assert!(!is_feature_allowed("web-sync", EDITION_BASE));
+        assert!(!is_feature_allowed("cloud-backup", EDITION_BASE));
+    }
+
+    #[test]
+    fn unknown_feature_denied() {
+        assert!(!is_feature_allowed("nonexistent", EDITION_PREMIUM));
+    }
+}

src-tauri/src/commands/license_commands.rs

@@ -0,0 +1,426 @@
+// License validation, storage and reading for the Base/Premium editions.
+//
+// Architecture:
+// - License key = "SR-BASE-<JWT>" or "SR-PREMIUM-<JWT>", JWT signed Ed25519 by the server
+// - Activation token = separate JWT, also signed by the server, binds the license to a machine
+//   (machine_id claim must match the local machine_id). Without it, a copied license.key would
+//   work on any machine. Activation tokens are issued by the server in a separate flow (Issue #49).
+// - Both files live in app_data_dir/ — license.key and activation.token
+// - get_edition() returns "free" unless BOTH license JWT is valid (signature + exp) AND
+//   either there is no activation token (graceful pre-activation state) OR the activation token
+//   matches the local machine_id.
+//
+// CWE-613: every license JWT MUST carry an `exp` claim. We reject licenses without it.
+
+use jsonwebtoken::{decode, Algorithm, DecodingKey, Validation};
+use serde::{Deserialize, Serialize};
+use std::fs;
+use std::path::PathBuf;
+use tauri::Manager;
+
+use super::entitlements::{EDITION_BASE, EDITION_FREE, EDITION_PREMIUM};
+
+// Ed25519 public key for license verification.
+//
+// IMPORTANT: this PEM is a development placeholder taken from RFC 8410 §10.3 test vectors.
+// The matching private key is publicly known, so any license signed with it offers no real
+// protection. Replace this constant with the production public key before shipping a paid
+// release. The corresponding private key MUST live only on the license server (Issue #49).
+const PUBLIC_KEY_PEM: &str = "-----BEGIN PUBLIC KEY-----\n\
+MCowBQYDK2VwAyEAGb9ECWmEzf6FQbrBZ9w7lshQhqowtrbLDFw4rXAxZuE=\n\
+-----END PUBLIC KEY-----\n";
+
+const LICENSE_FILE: &str = "license.key";
+const ACTIVATION_FILE: &str = "activation.token";
+
+const KEY_PREFIX_BASE: &str = "SR-BASE-";
+const KEY_PREFIX_PREMIUM: &str = "SR-PREMIUM-";
+
+/// Decoded license metadata exposed to the frontend.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct LicenseInfo {
+    pub edition: String,
+    pub email: String,
+    pub features: Vec<String>,
+    pub machine_limit: u32,
+    pub issued_at: i64,
+    pub expires_at: i64,
+}
+
+/// Claims embedded in the license JWT (signed by the license server).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+struct LicenseClaims {
+    sub: String, // email
+    iss: String,
+    iat: i64,
+    exp: i64, // mandatory — see CWE-613
+    edition: String,
+    #[serde(default)]
+    features: Vec<String>,
+    machine_limit: u32,
+}
+
+/// Claims embedded in the activation token JWT (server-signed, machine-bound).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+struct ActivationClaims {
+    sub: String, // license id or hash
+    iat: i64,
+    exp: i64,
+    machine_id: String,
+}
+
+fn app_data_dir(app: &tauri::AppHandle) -> Result<PathBuf, String> {
+    app.path()
+        .app_data_dir()
+        .map_err(|e| format!("Cannot get app data dir: {}", e))
+}
+
+fn license_path(app: &tauri::AppHandle) -> Result<PathBuf, String> {
+    Ok(app_data_dir(app)?.join(LICENSE_FILE))
+}
+
+fn activation_path(app: &tauri::AppHandle) -> Result<PathBuf, String> {
+    Ok(app_data_dir(app)?.join(ACTIVATION_FILE))
+}
+
+/// Strip the human-readable prefix and return the bare JWT.
+fn strip_prefix(key: &str) -> Result<&str, String> {
+    let trimmed = key.trim();
+    if let Some(jwt) = trimmed.strip_prefix(KEY_PREFIX_BASE) {
+        return Ok(jwt);
+    }
+    if let Some(jwt) = trimmed.strip_prefix(KEY_PREFIX_PREMIUM) {
+        return Ok(jwt);
+    }
+    Err("License key must start with SR-BASE- or SR-PREMIUM-".to_string())
+}
+
+/// Pure validation: decode the JWT, verify signature against `public_key_pem`, ensure the
+/// edition claim is one we recognize. Returns `LicenseInfo` on success.
+///
+/// Separated from the Tauri command so tests can pass their own key.
+fn validate_with_key(key: &str, public_key_pem: &[u8]) -> Result<LicenseInfo, String> {
+    let jwt = strip_prefix(key)?;
+
+    let decoding_key = DecodingKey::from_ed_pem(public_key_pem)
+        .map_err(|e| format!("Invalid public key: {}", e))?;
+
+    let mut validation = Validation::new(Algorithm::EdDSA);
+    // jsonwebtoken validates `exp` by default; assert this explicitly so a future config
+    // change cannot silently disable it (CWE-613).
+    validation.validate_exp = true;
+    validation.leeway = 0;
+    validation.set_required_spec_claims(&["exp", "iat"]);
+
+    let data = decode::<LicenseClaims>(jwt, &decoding_key, &validation)
+        .map_err(|e| format!("Invalid license: {}", e))?;
+
+    let claims = data.claims;
+    if claims.edition != EDITION_BASE && claims.edition != EDITION_PREMIUM {
+        return Err(format!("Unknown edition '{}'", claims.edition));
+    }
+
+    Ok(LicenseInfo {
+        edition: claims.edition,
+        email: claims.sub,
+        features: claims.features,
+        machine_limit: claims.machine_limit,
+        issued_at: claims.iat,
+        expires_at: claims.exp,
+    })
+}
+
+/// Validate an activation token against the local machine. The token must be signed by the
+/// license server and its `machine_id` claim must match the local machine identifier.
+fn validate_activation_with_key(
+    token: &str,
+    local_machine_id: &str,
+    public_key_pem: &[u8],
+) -> Result<(), String> {
+    let decoding_key = DecodingKey::from_ed_pem(public_key_pem)
+        .map_err(|e| format!("Invalid public key: {}", e))?;
+
+    let mut validation = Validation::new(Algorithm::EdDSA);
+    validation.validate_exp = true;
+    validation.leeway = 0;
+    validation.set_required_spec_claims(&["exp", "iat"]);
+
+    let data = decode::<ActivationClaims>(token.trim(), &decoding_key, &validation)
+        .map_err(|e| format!("Invalid activation token: {}", e))?;
+
+    if data.claims.machine_id != local_machine_id {
+        return Err("Activation token belongs to a different machine".to_string());
+    }
+    Ok(())
+}
+
+// === Tauri commands ===========================================================================
+
+/// Validate a license key without persisting it. Used by the UI to give immediate feedback
+/// before the user confirms storage.
+#[tauri::command]
+pub fn validate_license_key(key: String) -> Result<LicenseInfo, String> {
+    validate_with_key(&key, PUBLIC_KEY_PEM.as_bytes())
+}
+
+/// Persist a previously-validated license key to disk. The activation token (machine binding)
+/// is stored separately by [`store_activation_token`] once the server has issued one.
+#[tauri::command]
+pub fn store_license(app: tauri::AppHandle, key: String) -> Result<LicenseInfo, String> {
+    let info = validate_with_key(&key, PUBLIC_KEY_PEM.as_bytes())?;
+    let path = license_path(&app)?;
+    if let Some(parent) = path.parent() {
+        fs::create_dir_all(parent).map_err(|e| format!("Cannot create app data dir: {}", e))?;
+    }
+    fs::write(&path, key.trim()).map_err(|e| format!("Cannot write license file: {}", e))?;
+    Ok(info)
+}
+
+/// Persist a server-issued activation token (machine binding). The token is opaque to the
+/// caller — it must validate against the local machine_id to be considered active.
+#[tauri::command]
+pub fn store_activation_token(app: tauri::AppHandle, token: String) -> Result<(), String> {
+    let local_id = machine_id_internal()?;
+    validate_activation_with_key(&token, &local_id, PUBLIC_KEY_PEM.as_bytes())?;
+    let path = activation_path(&app)?;
+    if let Some(parent) = path.parent() {
+        fs::create_dir_all(parent).map_err(|e| format!("Cannot create app data dir: {}", e))?;
+    }
+    fs::write(&path, token.trim()).map_err(|e| format!("Cannot write activation file: {}", e))
+}
+
+/// Read the stored license without revalidating. Returns `None` when no license is present.
+/// The returned info is only structurally decoded — call [`get_edition`] for the gating value.
+#[tauri::command]
+pub fn read_license(app: tauri::AppHandle) -> Result<Option<LicenseInfo>, String> {
+    let path = license_path(&app)?;
+    if !path.exists() {
+        return Ok(None);
+    }
+    let key = fs::read_to_string(&path).map_err(|e| format!("Cannot read license file: {}", e))?;
+    Ok(validate_with_key(&key, PUBLIC_KEY_PEM.as_bytes()).ok())
+}
+
+/// Returns the active edition (`"free"`, `"base"`, or `"premium"`) for use by feature gates.
+///
+/// Returns "free" when:
+/// - no license is stored,
+/// - the license JWT is invalid or expired,
+/// - an activation token exists but does not match this machine.
+///
+/// Note: a missing activation token is treated as a graceful pre-activation state and does
+/// NOT downgrade the edition. Server-side activation happens later (Issue #53).
+#[tauri::command]
+pub fn get_edition(app: tauri::AppHandle) -> Result<String, String> {
+    Ok(current_edition(&app))
+}
+
+/// Internal helper used by `entitlements::check_entitlement`. Never returns an error — any
+/// failure resolves to "free" so feature gates fail closed.
+pub(crate) fn current_edition(app: &tauri::AppHandle) -> String {
+    let Ok(path) = license_path(app) else {
+        return EDITION_FREE.to_string();
+    };
+    if !path.exists() {
+        return EDITION_FREE.to_string();
+    }
+    let Ok(key) = fs::read_to_string(&path) else {
+        return EDITION_FREE.to_string();
+    };
+    let Ok(info) = validate_with_key(&key, PUBLIC_KEY_PEM.as_bytes()) else {
+        return EDITION_FREE.to_string();
+    };
+
+    // If an activation token exists, it must match the local machine. A missing token is
+    // accepted (graceful pre-activation).
+    if let Ok(activation_path) = activation_path(app) {
+        if activation_path.exists() {
+            let Ok(token) = fs::read_to_string(&activation_path) else {
+                return EDITION_FREE.to_string();
+            };
+            let Ok(local_id) = machine_id_internal() else {
+                return EDITION_FREE.to_string();
+            };
+            if validate_activation_with_key(&token, &local_id, PUBLIC_KEY_PEM.as_bytes()).is_err()
+            {
+                return EDITION_FREE.to_string();
+            }
+        }
+    }
+
+    info.edition
+}
+
+/// Cross-platform machine identifier. Stable across reboots; will change after an OS reinstall
+/// or hardware migration, in which case the user must re-activate (handled in Issue #53).
+#[tauri::command]
+pub fn get_machine_id() -> Result<String, String> {
+    machine_id_internal()
+}
+
+fn machine_id_internal() -> Result<String, String> {
+    machine_uid::get().map_err(|e| format!("Cannot read machine id: {}", e))
+}
+
+// === Tests ====================================================================================
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ed25519_dalek::pkcs8::{EncodePrivateKey, EncodePublicKey, LineEnding};
+    use ed25519_dalek::SigningKey;
+    use jsonwebtoken::{encode, EncodingKey, Header};
+
+    /// Build a deterministic test keypair so signed tokens are reproducible across runs.
+    fn test_keypair() -> (String, String) {
+        let seed = [42u8; 32];
+        let signing_key = SigningKey::from_bytes(&seed);
+        let verifying_key = signing_key.verifying_key();
+        let private_pem = signing_key
+            .to_pkcs8_pem(LineEnding::LF)
+            .unwrap()
+            .to_string();
+        let public_pem = verifying_key.to_public_key_pem(LineEnding::LF).unwrap();
+        (private_pem, public_pem)
+    }
+
+    fn make_token(private_pem: &str, claims: &LicenseClaims) -> String {
+        let key = EncodingKey::from_ed_pem(private_pem.as_bytes()).unwrap();
+        encode(&Header::new(Algorithm::EdDSA), claims, &key).unwrap()
+    }
+
+    fn make_activation_token(private_pem: &str, claims: &ActivationClaims) -> String {
+        let key = EncodingKey::from_ed_pem(private_pem.as_bytes()).unwrap();
+        encode(&Header::new(Algorithm::EdDSA), claims, &key).unwrap()
+    }
+
+    fn now() -> i64 {
+        std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap()
+            .as_secs() as i64
+    }
+
+    #[test]
+    fn rejects_key_without_prefix() {
+        let (_priv, public_pem) = test_keypair();
+        let result = validate_with_key("nonsense", public_pem.as_bytes());
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn accepts_well_formed_base_license() {
+        let (private_pem, public_pem) = test_keypair();
+        let claims = LicenseClaims {
+            sub: "user@example.com".to_string(),
+            iss: "lacompagniemaximus.com".to_string(),
+            iat: now(),
+            exp: now() + 86400,
+            edition: EDITION_BASE.to_string(),
+            features: vec!["auto-update".to_string()],
+            machine_limit: 3,
+        };
+        let jwt = make_token(&private_pem, &claims);
+        let key = format!("{}{}", KEY_PREFIX_BASE, jwt);
+        let info = validate_with_key(&key, public_pem.as_bytes()).unwrap();
+        assert_eq!(info.edition, EDITION_BASE);
+        assert_eq!(info.email, "user@example.com");
+        assert_eq!(info.machine_limit, 3);
+    }
+
+    #[test]
+    fn rejects_expired_license() {
+        let (private_pem, public_pem) = test_keypair();
+        let claims = LicenseClaims {
+            sub: "user@example.com".to_string(),
+            iss: "lacompagniemaximus.com".to_string(),
+            iat: now() - 1000,
+            exp: now() - 100,
+            edition: EDITION_BASE.to_string(),
+            features: vec![],
+            machine_limit: 3,
+        };
+        let jwt = make_token(&private_pem, &claims);
+        let key = format!("{}{}", KEY_PREFIX_BASE, jwt);
+        let result = validate_with_key(&key, public_pem.as_bytes());
+        assert!(result.is_err(), "expired license must be rejected");
+    }
+
+    #[test]
+    fn rejects_license_signed_with_wrong_key() {
+        let (private_pem, _public_pem) = test_keypair();
+        // Generate a different keypair to verify with
+        let other_seed = [7u8; 32];
+        let other_signing = SigningKey::from_bytes(&other_seed);
+        let other_public = other_signing
+            .verifying_key()
+            .to_public_key_pem(LineEnding::LF)
+            .unwrap();
+        let claims = LicenseClaims {
+            sub: "user@example.com".to_string(),
+            iss: "lacompagniemaximus.com".to_string(),
+            iat: now(),
+            exp: now() + 86400,
+            edition: EDITION_BASE.to_string(),
+            features: vec![],
+            machine_limit: 3,
+        };
+        let jwt = make_token(&private_pem, &claims);
+        let key = format!("{}{}", KEY_PREFIX_BASE, jwt);
+        let result = validate_with_key(&key, other_public.as_bytes());
+        assert!(result.is_err(), "wrong-key signature must be rejected");
+    }
+
+    #[test]
+    fn rejects_corrupted_jwt() {
+        let (_priv, public_pem) = test_keypair();
+        let key = format!("{}not.a.real.jwt", KEY_PREFIX_BASE);
+        let result = validate_with_key(&key, public_pem.as_bytes());
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn rejects_unknown_edition() {
+        let (private_pem, public_pem) = test_keypair();
+        let claims = LicenseClaims {
+            sub: "user@example.com".to_string(),
+            iss: "lacompagniemaximus.com".to_string(),
+            iat: now(),
+            exp: now() + 86400,
+            edition: "enterprise".to_string(),
+            features: vec![],
+            machine_limit: 3,
+        };
+        let jwt = make_token(&private_pem, &claims);
+        let key = format!("{}{}", KEY_PREFIX_BASE, jwt);
+        let result = validate_with_key(&key, public_pem.as_bytes());
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn activation_token_matches_machine() {
+        let (private_pem, public_pem) = test_keypair();
+        let claims = ActivationClaims {
+            sub: "license-id".to_string(),
+            iat: now(),
+            exp: now() + 86400,
+            machine_id: "this-machine".to_string(),
+        };
+        let token = make_activation_token(&private_pem, &claims);
+        assert!(validate_activation_with_key(&token, "this-machine", public_pem.as_bytes()).is_ok());
+    }
+
+    #[test]
+    fn activation_token_rejects_other_machine() {
+        let (private_pem, public_pem) = test_keypair();
+        let claims = ActivationClaims {
+            sub: "license-id".to_string(),
+            iat: now(),
+            exp: now() + 86400,
+            machine_id: "machine-A".to_string(),
+        };
+        let token = make_activation_token(&private_pem, &claims);
+        let result = validate_activation_with_key(&token, "machine-B", public_pem.as_bytes());
+        assert!(result.is_err(), "copied activation token must be rejected");
+    }
+}

src-tauri/src/commands/mod.rs

@@ -1,7 +1,11 @@
-pub mod fs_commands;
+pub mod entitlements;
 pub mod export_import_commands;
+pub mod fs_commands;
+pub mod license_commands;
 pub mod profile_commands;
 
-pub use fs_commands::*;
+pub use entitlements::*;
 pub use export_import_commands::*;
+pub use fs_commands::*;
+pub use license_commands::*;
 pub use profile_commands::*;

src-tauri/src/lib.rs

@@ -114,6 +114,13 @@ pub fn run() {
             commands::hash_pin,
             commands::verify_pin,
             commands::repair_migrations,
+            commands::validate_license_key,
+            commands::store_license,
+            commands::store_activation_token,
+            commands::read_license,
+            commands::get_edition,
+            commands::get_machine_id,
+            commands::check_entitlement,
         ])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");