Add SCRAM-SHA-1 and SCRAM-SHA-256 support via libgsasl

[jas4711]

Hi! SCRAM offers some advantages compared to CRAM-MD5/DIGEST-MD5, and this is a proof-of-concept patch to add support for it via libgsasl. I am looking for help and review with the patch.

[bagder]

Within days I'd say.

[bagder]

Thanks!

[vszakats]

Getting these errors and warnings when building against latest stable libgsasl 1.10.0 [UPDATE: there is a newer, 1.11.0, alpha versions, that answers some questions below.]:

clang -I. -I../include -I"../../nghttp2/pkg/usr/local/include" -I"../../libssh2/include" -I"../../libssh2/win32" -I"../../openssl/include" -I"../../zlib/pkg/usr/local" -I"../../zstd/build/cmake/pkg/usr/local/include" -I"../../libgsasl/pkg/usr/local/include" -target x86_64-w64-mingw32 --sysroot /usr/local/opt/mingw-w64/toolchain-x86_64 -DCURL_STATICLIB -DCURL_ENABLE_MQTT -fno-ident -DHAVE_ATOMIC -DUSE_HSTS -DUNICODE -D_UNICODE -DCURL_DISABLE_OPENSSL_AUTO_LOAD_CONFIG -DNGHTTP2_STATICLIB -g -O2 -Wall -W -fno-strict-aliasing -m64 -D_AMD64_ -DBUILDING_LIBCURL -DCURL_WITH_MULTI_SSL -DUSE_NGHTTP2 -DUSE_LIBSSH2 -DHAVE_LIBSSH2_H -DUSE_OPENSSL -DHAVE_OPENSSL_PKCS12_H -DOPENSSL_NO_KRB5 -DHAVE_OPENSSL_SRP -DUSE_TLS_SRP -DUSE_SCHANNEL -DHAVE_LIBZ -DHAVE_ZLIB_H -DHAVE_ZSTD -DUSE_WIN32_IDN -DWANT_IDN_PROTOTYPES -DUSE_GSASL -DUSE_WINDOWS_SSPI -DENABLE_IPV6 -D_WIN32_WINNT=0x0501 -DHAVE_LDAP_SSL -c vauth/krb5_gssapi.c -o vauth/krb5_gssapi.o
vauth/gsasl.c:70:7: error: assigning to 'int' from incompatible type 'void'
  res =
      ^
vauth/gsasl.c:75:63: error: use of undeclared identifier 'result'
    failf(data, "setting AUTHID failed: %s\n", gsasl_strerror(result));
                                                              ^
vauth/gsasl.c:81:7: error: assigning to 'int' from incompatible type 'void'
  res =
      ^
vauth/gsasl.c:86:65: error: use of undeclared identifier 'result'
    failf(data, "setting PASSWORD failed: %s\n", gsasl_strerror(result));
                                                                ^
vauth/gsasl.c:111:38: warning: passing 'unsigned char *' to parameter of type 'const char *' converts between pointers to integer types with different sign [-Wpointer-sign]
  result = gsasl_step(gsasl->client, chlg, chlglen, &response, outlen);
                                     ^~~~
../../libgsasl/pkg/usr/local/include/gsasl.h:445:20: note: passing argument to parameter 'input' here
                                   const char *input, size_t input_len,
                                               ^
vauth/gsasl.c:101:10: warning: unused variable 'chlg64len' [-Wunused-variable]
  size_t chlg64len = chlg64 ? strlen(chlg64) : 0;
         ^
2 warnings and 4 errors generated.
make[1]: *** [vauth/gsasl.o] Error 1

One is trivial to fix by renaming result references to res, but the rest raises questions, e.g. gsasl_property_set() returns void with GSASL_VERSION_NUMBER == 0x010a00.
[UPDATE: The correct condition is GSASL_VERSION_NUMBER >= 0x010a01. Would be nice to apply it to the NEWS entry of libgsasl as well. So the remaining question is the unused variable chlg64len.]

PR fixing the simpler ones: #6587

[jas4711]

The API change is in the 1.11.x branch, and not in 1.10.x, so I think the check should be GSASL_VERSION_NUMBER >= 0x010b00 -- sorry about that!

I think the other issues are resolved? I can't really tell what is open and what is resolved. Thanks for merging, btw!