SHA-1 certificates are expected to be gone by January 1st, 2017. By then, more and more servers will have ported their certificates to the SHA-2 variety, so expect more HTTPS connection failures for WinHttp under Windows XP & Windows Vista. It makes sense, after all; support for Windows XP finally came to an end on April 8, 2014 (Microsoft had already dropped support for Windows Vista) and the last Windows OS not supporting TLS 1.1 & 1.2, Windows Server 2008, reached end of mainstream support this January.