- POST /refresh_token: accept current Bearer token (or Cookie fallback),
verify RSA signature, check grace window (iat + keep_time * multiplier)
and refresh count limit, then issue a new token.
- Token payload extended with iat, refresh_count, max_refresh fields.
- iat preserves original issue time; created_at updates on each refresh.
- Rate limited: 5 req / 5 min / IP via RateLimiter.
- Config: Token.refresh_grace_multiplier (default 2), Token.max_refresh (default 10).
- Backward compatible: old tokens without new fields still pass proxy checks.
qing
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