C# Signature:

/// <summary>
/// This function implements the Web Proxy Auto-Discovery (WPAD) protocol for automatically configuring the proxy settings for an HTTP request. The WPAD protocol downloads a Proxy Auto-Configuration (PAC) file, which is a script that identifies the proxy server to use for a given target URL. PAC files are typically deployed by the IT department within a corporate network environment. The URL of the PAC file can either be specified explicitly or WinHttpGetProxyForUrl can be instructed to automatically discover the location of the PAC file on the local network.
/// </summary>
/// <param name="hSession">The WinHTTP session handle returned by the WinHttpOpen function</param>
/// <param name="lpcwszUrl">A pointer to a null-terminated Unicode string that contains the URL of the HTTP request that the application is preparing to send.</param>
/// <param name="pAutoProxyOptions">A pointer to a WINHTTP_AUTOPROXY_OPTIONS structure that specifies the auto-proxy options to use.</param>
/// <param name="pProxyInfo">A pointer to a WINHTTP_PROXY_INFO structure that receives the proxy setting. This structure is then applied to the request handle using the WINHTTP_OPTION_PROXY option.</param>
/// <returns>If the function succeeds, the function returns <c>true</c>. If the function fails, it returns <c>false</c>. For extended error data, call <see cref="System.Runtime.InteropServices.Marshal.GetLastWin32Error"/>.</returns>
[DllImport("winhttp.dll", SetLastError = true, CharSet = CharSet.Unicode)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool WinHttpGetProxyForUrl(IntPtr hSession, string lpcwszUrl, ref WINHTTP_AUTOPROXY_OPTIONS pAutoProxyOptions, ref WINHTTP_PROXY_INFO pProxyInfo);

VB Signature:

Declare Function WinHttpGetProxyForUrl Lib "winhttp.dll" (TODO) As TODO

User-Defined Types:

None.

Alternative Managed API:

Do you know one? Please contribute it!

Notes:

Minimum supported client: Windows XP, Windows 2000 Professional with SP3 [desktop apps only]

Minimum supported server: Windows Server 2003, Windows 2000 Server with SP3 [desktop apps only]

Tips & Tricks:

Please add some!

Sample Code:

https://msdn.microsoft.com/en-us/library/windows/desktop/aa384122(v=vs.85).aspx