Before this change, `license_commands::check_account_edition` read
`account.json` directly and granted Premium when `subscription_status`
was `"active"`. Any local process could write that JSON and bypass
the paywall without ever touching the Logto session.
Introduce `account_cache` with:
- `save(app, &AccountInfo)` — signs the serialised AccountInfo with
HMAC-SHA256 and writes a `{"data", "sig"}` envelope. The 32-byte
key lives in the OS keychain (service `com.simpl.resultat`, user
`account-hmac-key`) alongside the OAuth tokens from #78.
- `load_unverified` — accepts both signed and legacy payloads for UI
display (name, email, picture). The license path must never use
this.
- `load_verified` — requires a valid HMAC signature; returns None for
legacy payloads, missing keychain, tampered data. Used by
`check_account_edition` so Premium stays locked until the next
token refresh re-signs the cache.
- `delete` — wipes both the file and the keychain key on logout so
the next session generates a fresh cryptographic anchor.
`auth_commands::handle_auth_callback` and `refresh_auth_token` now
call `account_cache::save` instead of writing the file directly.
`logout` clears both stores. `get_account_info` delegates to
`load_unverified` so upgraded users see their profile immediately.
Trust boundary: the HMAC key lives in the keychain and shares its
security model with the OAuth tokens. If the keychain is unreachable,
the gating path refuses to grant Premium (fail-closed), which matches
the store_mode policy introduced in #78.
Refs #66, CWE-345
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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