突然發現 yahoo 不支援 SSL3.0 或 TLS 1.0 了, 要改用 TLS 1.2 才抓的到網頁資料

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            ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

            ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;

.Net 4.0 在抓網頁之前先加這兩行, 就可以了. 

.Net 4.5 支援 Tls12, 可以用 

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            ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

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