RemoteCertificateNameMismatch, RemoteCertificateChainErrors with HttpClient

Question

Hello everyone and thanks for the help in advance. I am refactoring code that previously used WebClient (now deprecated) to HttpClient. The page connects with to a device using a self-signed certificate with an internal IP address for the Uri. Therefore the device is trusted. Previously, using WebClient, I used the following:

However, 


                using (var client = new HttpClient(handler))
                {
                    ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
                    byte[] fileBytes = await client.GetByteArrayAsync(uri);
                    File.WriteAllBytes(CSVPath, fileBytes);
                }

throws RemoteCertificateNameMismatch, RemoteCertificateChainErrors

Answer 1

Hi @Kmcnet,

First, I looked up the documentation at Microsoft Docs and tested the examples.

Then I looked at the information of the relevant code, and there are no variables involved here. So I brought your code straight in for testing.

I found that your code can't read the information in the URL.

I think you can modify the code a bit:

HttpClientHandler handler = new HttpClientHandler { Credentials = new NetworkCredential(UserName, Password) };
handler.ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => true;
using (var client = new HttpClient(handler))
                {
                    ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
                    byte[] fileBytes = await client.GetByteArrayAsync(uri);
                    File.WriteAllBytes(CSVPath, fileBytes);
                }

change to

HttpClientHandler handler = new HttpClientHandler { Credentials = new NetworkCredential(UserName, Password) };
handler.ServerCertificateCustomValidationCallback = ServerCertificateCustomValidation;
using (var client = new HttpClient(handler))
                {
                   
                    byte[] fileBytes = await client.GetByteArrayAsync(uri);
                    File.WriteAllBytes(CSVPath, fileBytes);
                }

For more you can check out the documentation:

Document

Of course, this could also be an issue with the URL.

Best Regards

Qi You

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Answer 2

You need to declare a handler, then add the certificate override to the handler.

HttpClientHandler handler = new HttpClientHandler { Credentials = new NetworkCredential(UserName, Password) };
handler.ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => true;

Answer 3

You need to declare a handler, then add the certificate override to the handler:

handler.ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => true;