场景： 限制仅能通过IAM角色sso-admin来访问NAT网关。
策略示例：

{
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "natgateway:*"
      ],
      "Resource": [
        "*"
      ],
      "Condition":{
          "StringEquals":{
                  "volc:PrincipalTrn":"trn:iam::20000123**:role/sso-admin"
          }
      }
    }
  ]
}