public boolean isExpired() {
            return System.currentTimeMillis() >= expires;
        }
Returns whether this specific cached value has expired. Expired
values will be automatically refreshed by CachedVaultSecretService.

@return
    true if this cached value has expired, false otherwise.
extensions/guacamole-vault/modules/guacamole-vault-base/src/main/java/org/apache/guacamole/vault/secret/CachedVaultSecretService.java