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.
When CURL_DISABLE_CRYPTO_AUTH is defined the DIGEST-MD5 code should not
be included, regardless of whether USE__WINDOWS_SSPI is defined or not.
This is indicated by the definition of USE_HTTP_NEGOTIATE and USE_NTLM
in curl_setup.h.
