verify method
验证检查
Implementation
Future<void> verify() async {
// 首次使用
if (_signer == null) {
_signer = Signer(await credentials.call());
} else {
// 使用securityToken进行鉴权,则判断securityToken是否过期
if (_signer!.credentials.useSecurityToken) {
if (_signer!.credentials.expiration!.isBefore(DateTime.now().toUtc())) {
_signer = Signer(await credentials.call());
}
} else {
// expiration | securityToken中途丢失,则清空
_signer!.credentials.clearSecurityToken();
}
}
}