How Can I Access HTTPS APIs with Untrusted Certificates Using HttpClient?

Working with Untrusted Certificates in .NET HttpClient

Using HttpClient and HttpClientHandler to access HTTPS APIs can present challenges when dealing with self-signed or otherwise untrusted certificates. Unlike WebRequest, HttpClient doesn't directly support bypassing certificate validation in a straightforward manner.

This solution outlines how to handle untrusted certificates within a .NET Standard environment:

1. Create an HttpClientHandler:

<code class="language-csharp">var handler = new HttpClientHandler();</code>

2. Set ClientCertificateOptions:

<code class="language-csharp">handler.ClientCertificateOptions = ClientCertificateOption.Manual;</code>

3. Implement Custom Certificate Validation:

<code class="language-csharp">handler.ServerCertificateCustomValidationCallback = 
    (httpRequestMessage, cert, certChain, policyErrors) =>
{
    return true; // Accepts all certificates - use with caution!
};</code>

4. Create HttpClient with Custom Handler:

<code class="language-csharp">var client = new HttpClient(handler);</code>

Important Security Considerations:

This method disables certificate validation. While useful for development or testing, never use this in a production environment. Bypassing certificate validation exposes your application to significant security risks, including man-in-the-middle attacks. Always prioritize using trusted certificates for production applications to maintain security and data integrity.

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