Why curl Doesn’t Pick Up the Windows Browser Proxy

A Windows browser working through the company proxy does not establish that a libcurl-based application has discovered the same configuration. libcurl has documented proxy options and environment variables; Windows browser proxy discovery is another interface.

An application that wants to follow the current user's Windows settings can query them using the Windows proxy-configuration API. That still leaves work to do. An automatic-configuration URL points to a PAC policy, not a fixed proxy endpoint suitable for copying directly into CURLOPT_PROXY.

Manual proxy setting

Parse the supported configuration and supply the appropriate proxy and bypass options to the client.

PAC or automatic discovery

Evaluate the policy for the actual destination using a supported integration.

Background service

Check which account owns the effective configuration; the interactive user's settings may not be the service's settings.

For a small diagnostic request, an explicit libcurl proxy option removes discovery from the comparison. A bounded curl command can check the same HTTP endpoint independently. For a managed application, implement the intended discovery policy rather than relying on a browser's successful request as proof of shared configuration.