.NET Core 使用 HttpClient SSL 請求出錯的解決辦法

問題

使用 HTTP Client 請求 HTTPS 的 API 時出現 The certificate cannot be verified up to a trusted certification authority 異常，並且證書已經傳入。

下面就是問題代碼：

public class Program
{
	public static void Main(string[] args)
	{
		var url = @"https://xxx.xxx.xxx.xxx:xxxx/xxx-web/services/xxxx?wsdl";

		var handler = new HttpClientHandler
		{
			ClientCertificateOptions = ClientCertificateOption.Manual,
			ClientCertificates =
			{
				new X509Certificate2(@"E:\cert\rootTrust.cer","11111111"),
				new X509Certificate2(@"E:\cert\middleTrust.cer","11111111"),
				new X509Certificate2(@"E:\cert\wskey.pfx","ws654321")
			}
		};
		
		var webRequest = new HttpClient(handler);
		var result = webRequest.GetStringAsync(url).GetAwaiter().GetResult();
		Console.WriteLine(result);
	}
}

原因

因為在發出 HTTPS 請求的時候，HttpClient 都會檢查 SSL 證書是否合法。如果不合法的話，就會導致拋出異常信息，而對方給出的證書是自簽發的測試接口的證書，所以不是一個合法的 SSL 證書。

解決

在 HttpClientHandler 當中會有一個 ServerCertificateCustomValidationCallback 事件，該事件用於判定證書驗證是否通過。我們可以掛接該事件，然后邏輯編寫為直接返回 true 結果，這樣就會忽略掉證書異常的情況。

最新的代碼如下：

public class Program
{
	public static void Main(string[] args)
	{
		var url = @"https://xxx.xxx.xxx.xxx:xxxx/xxx-web/services/xxxx?wsdl";

		var handler = new HttpClientHandler
		{
			ServerCertificateCustomValidationCallback = (message, certificate2, arg3, arg4) => true, 
			ClientCertificateOptions = ClientCertificateOption.Manual,
			ClientCertificates =
			{
				new X509Certificate2(@"E:\cert\rootTrust.cer","11111111"),
				new X509Certificate2(@"E:\cert\middleTrust.cer","11111111"),
				new X509Certificate2(@"E:\cert\wskey.pfx","ws654321")
			}
		};
		
		var webRequest = new HttpClient(handler);
		var result = webRequest.GetStringAsync(url).GetAwaiter().GetResult();
		Console.WriteLine("xx");
	}
}