public void login(final List<String> servers) {
        if ((System.currentTimeMillis() - lastRefreshTime) < (tokenExpiredTime - tokenRefreshWindow)) {
            return;
        }
        for (String server : servers) {
            if (this.doLogin(server)) {
                this.lastRefreshTime = System.currentTimeMillis();
                return;
            }
        }
    }
server login.

@param servers server list.
shenyu-sync-data-center/shenyu-sync-data-http/src/main/java/org/apache/shenyu/sync/data/http/AccessTokenManager.java