本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# 步驟 2：建立撤銷連線函數
<a name="create-revocation-connection-function"></a>

建立連線函數，根據 KeyValueStore 檢查憑證序號，以判斷憑證是否遭到撤銷。

建立連線函數，根據 KeyValueStore 檢查憑證序號：

```
aws cloudfront create-connection-function \
  --name "revocation-control" \
  --connection-function-config file://connection-function-config.json \
  --connection-function-code file://connection-function-code.txt
```

組態檔案會指定 KeyValueStore 關聯：

```
{
  "Runtime": "cloudfront-js-2.0",
  "Comment": "A function that implements revocation control via KVS",
  "KeyValueStoreAssociations": {
    "Quantity": 1,
    "Items": [
      {
        "KeyValueStoreArn": "arn:aws:cloudfront::account-id:key-value-store/kvs-id"
      }
    ]
  }
}
```

Connection Function 程式碼會檢查 KeyValueStore 是否有已撤銷的憑證：

```
import cf from 'cloudfront';

async function connectionHandler(connection) {
    const kvsHandle = cf.kvs();
    
    // Get parsed client serial number from client certificate
    const clientSerialNumber = connection.clientCertInfo.serialNumber;
    
    // Check KVS to see if serial number exists as a key
    const serialNumberExistsInKvs = await kvsHandle.exists(clientSerialNumber);
    
    // Deny connection if serial number exists in KVS
    if (serialNumberExistsInKvs) {
        console.log("Connection denied - certificate revoked");
        return connection.deny();
    }
    
    // Allow connections that don't exist in kvs
    console.log("Connection allowed");
    return connection.allow();
}
```