Curl_sasl_create_digest_md5_message() would simply cast the SPN variable
to a TCHAR when calling InitializeSecurityContext(). This meant that,
under Unicode builds, it would not be valid wide character string.

Updated to use the recently introduced Curl_sasl_build_spn() function
which performs the correct conversion for us.

Various parts of the libcurl source code build a SPN for inclusion in
authentication data. This information is either used by our own native
generation routines or passed to authentication functions in third-party
libraries such as SSPI. However, some of these instances use fixed
buffers rather than dynamically allocated ones and not all of those that
should, convert to wide character strings in Unicode builds.

Implemented a common function that generates a SPN and performs the
wide character conversion where necessary.

Curl_sasl_create_digest_md5_message() wouldn't free the Package Info
structure after QuerySecurityPackageInfo() had allocated it.

Reflect recent changes in SPNEGO and GSS-API code in the docs.
Update them with appropriate namings and remove visible spots for
GSS-Negotiate.

Following the recent changes and in attempt to align the SSPI based
authentication code performed the following:

* Use NULL and SECBUFFVERSION rather than hard coded constants.
* Avoid comparison of zero in if statements.
* Standardised the buf and desc setup code.

vtls.c:688:43: warning: unused parameter 'data'

warning: `orig_opt' might be used uninitialized in this function

Given the SSPI package info query indicates a token size of 2888 bytes,
and as with the Winbind code and commit 9008f3d5, use a dynamic buffer
for the Type-1 and Type-3 message generation rather than a fixed buffer
of 1024 bytes.

Just as with the SSPI implementations of Digest and Negotiate added a
package info query so that libcurl can a) return a more appropriate
error code when the NTLM package is not supported and b) it can be of
use later to allocate a dynamic buffer for the Type-1 and Type-3
output tokens rather than use a fixed buffer of 1024 bytes.

OPENSSL_config() is "strongly recommended" to use but unfortunately that
function makes an exit() call on wrongly formatted config files which
makes it hard to use in some situations. OPENSSL_config() itself calls
CONF_modules_load_file() and we use that instead and we ignore its
return code!

Reported-by: Jan Ehrhardt
Bug: http://curl.haxx.se/bug/view.cgi?id=1401

Test case numbers with four digits have been available for a
while now.

Bug: http://curl.haxx.se/mail/lib-2014-06/0224.html
Reported-by: Leonardo Rosati

If the server rejects our authentication attempt and curl hasn't
called CompleteAuthToken() then the status variable will be
SEC_I_CONTINUE_NEEDED and not SEC_E_OK.

As such the existing detection mechanism for determining whether or not
the authentication process has finished is not sufficient.

However, the WWW-Authenticate: Negotiate header line will not contain
any data when the server has exhausted the negotiation, so we can use
that coupled with the already allocated context pointer.

The GetDarwinVersionNumber() function uses strtok, which is not
thread-safe.

This seems to be the way it should work. Right now we can't build with
BoringSSL and try this out properly due to a minor API breakage.

LibreSSL is otherwise OpenSSL API compliant (so far)

To prevent infinite loop in readwrite_data() function when stream is
reset before any response body comes, reset closed flag to false once
it is evaluated to true.

"Expect: 100-continue", which was once deprecated in HTTP/2, is now
resurrected in HTTP/2 draft 14.  This change adds its support to
HTTP/2 code.  This change also includes stricter header field
checking.

Previously it only returned a CURLcode for errors, which is when it
returns a different size than what was passed in to it.

The http2 code only checked the curlcode and thus failed.

This function is available for every Windows version since Windows 95/NT.

reference:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa379942.aspx

... and has been so since 2005

Each backend now defines CURL_SSL_BACKEND accordingly. Added the *AXTLS
one which was missing previously.