lib/config-win32.h: let SMB/SMBS be enabled with OpenSSL/NSS

[vszakats]

The source code is now prepared to handle the case when both
Win32 Crypto and OpenSSL/NSS crypto backends are enabled
at the same time, making it possible to enable USE_WIN32_CRYPTO
whenever the targeted Windows version supports it. Since this
matches the minimum Windows version supported by curl
(Windows 2000), enable it unconditionally for the Win32 platform.

This in turn enables SMB (and SMBS) protocol support whenever
Win32 Crypto is available, regardless of what other crypto backends
are enabled.

Ref: #1840 (comment)

[jay]

You have changed it to use win32 crypto only if schannel but is that really what you meant? Aren't crypto and schannel two separate things, and now that there are changes in ntlm to handle win32 crypto properly can't we just enable USE_WIN32_CRYPTO all the time?

[vszakats]

I was going along @dscho's suggestion here, but, yes, as far as I can see the code, this macro is protecting crypto-only and unless I'm missing something NTLM-crypto-only functions (2-4 of them) throughout all lib sources. If this is correct, it could be enabled based on _WIN32.

[vszakats]

Since we're in config-win32.h, _WIN32 should always be defined, meaning that USE_WIN32_CRYPTO could just be enabled unconditionally in this header.

[vszakats]

USE_WIN32_CRYPTO requires: wincrypt.h, CryptAcquireContext(), CryptCreateHash(), CryptHashData(), CryptGetHashParam(), CryptDestroyHash(), CryptReleaseContext(), CryptImportKey(), CryptImportKey(), CryptDestroyKey().

As per MSDN, these are available starting Windows XP/2003, so the condition required is _WIN32_WINNT >= 0x0501.

[MarcelRaad]

@vszakats

As per MSDN, these are available starting Windows XP/2003

That's only because mentions of old unsupported OSs are regularly removed from the MSDN documentation. https://msdn.microsoft.com/en-us/library/ms867086.aspx says it's at least available since Windows NT 4 and Windows 95.

[jay]

FYI Windows 2000 has all those functions xported in advapi32. Whether they're actually declared or not for Windows 2k I don't know (yes in original mingw), but we've never had an os version check on that symbol before and people do build for Win2k at least according to the survey. I think if you remove the guard it will be fine. If someone is building for Windows 98 (how?) we can wait for feedback if it breaks for them.

edit: run it through CI just to be sure

[vszakats]

Okay, I'll commit that and wait for a green flag of course. MSDN tends to be unreliable for minimum versions, exactly like @MarcelRaad says.