spnego_sspi: add support for channel binding

Attempt to add support for Secure Channel binding when negotiate
authentication is used. The problem to solve is that by default IIS
accepts channel binding and curl doesn't utilise them. The result was a
401 response. Scope affects only the Schannel(winssl)-SSPI combination.

Fixes https://github.com/curl/curl/issues/3503
Closes https://github.com/curl/curl/pull/3509

lib/http_negotiate.c

@@ -89,6 +89,11 @@ CURLcode Curl_input_negotiate(struct connectdata *conn, bool proxy,
     }
   }
 
+  /* Supports SSL channel binding for Windows ISS extended protection */
+#if defined(USE_WINDOWS_SSPI) && defined(SECPKG_ATTR_ENDPOINT_BINDINGS)
+  neg_ctx->sslContext = conn->sslContext;
+#endif
+
   /* Initialize the security context and decode our challenge */
   result = Curl_auth_decode_spnego_message(data, userp, passwdp, service,
                                            host, header, neg_ctx);

lib/http_ntlm.c

@@ -175,6 +175,9 @@ CURLcode Curl_output_ntlm(struct connectdata *conn, bool proxy)
     if(s_hSecDll == NULL)
       return err;
   }
+#ifdef SECPKG_ATTR_ENDPOINT_BINDINGS
+  ntlm->sslContext = conn->sslContext;
+#endif
 #endif
 
   switch(ntlm->state) {

lib/urldata.h

@@ -364,6 +364,9 @@ struct negotiatedata {
   gss_buffer_desc output_token;
 #else
 #ifdef USE_WINDOWS_SSPI
+#ifdef SECPKG_ATTR_ENDPOINT_BINDINGS
+  CtxtHandle *sslContext;
+#endif
   DWORD status;
   CredHandle *credentials;
   CtxtHandle *context;
@@ -980,6 +983,9 @@ struct connectdata {
   void *seek_client;            /* pointer to pass to the seek() above */
 
   /*************** Request - specific items ************/
+#if defined(USE_WINDOWS_SSPI) && defined(SECPKG_ATTR_ENDPOINT_BINDINGS)
+  CtxtHandle *sslContext;
+#endif
 
 #if defined(USE_NTLM)
   struct ntlmdata ntlm;     /* NTLM differs from other authentication schemes

lib/vauth/spnego_sspi.c

@@ -92,7 +92,7 @@ CURLcode Curl_auth_decode_spnego_message(struct Curl_easy *data,
   size_t chlglen = 0;
   unsigned char *chlg = NULL;
   PSecPkgInfo SecurityPackage;
-  SecBuffer chlg_buf;
+  SecBuffer chlg_buf[2];
   SecBuffer resp_buf;
   SecBufferDesc chlg_desc;
   SecBufferDesc resp_desc;
@@ -191,10 +191,37 @@ CURLcode Curl_auth_decode_spnego_message(struct Curl_easy *data,
     /* Setup the challenge "input" security buffer */
     chlg_desc.ulVersion    = SECBUFFER_VERSION;
     chlg_desc.cBuffers     = 1;
-    chlg_desc.pBuffers  = &chlg_buf;
+    chlg_desc.pBuffers     = &chlg_buf[0];
-    chlg_buf.BufferType = SECBUFFER_TOKEN;
+    chlg_buf[0].BufferType = SECBUFFER_TOKEN;
-    chlg_buf.pvBuffer   = chlg;
+    chlg_buf[0].pvBuffer   = chlg;
-    chlg_buf.cbBuffer   = curlx_uztoul(chlglen);
+    chlg_buf[0].cbBuffer   = curlx_uztoul(chlglen);
+
+#ifdef SECPKG_ATTR_ENDPOINT_BINDINGS
+    /* ssl context comes from Schannel.
+    * When extended protection is used in IIS server,
+    * we have to pass a second SecBuffer to the SecBufferDesc
+    * otherwise IIS will not pass the authentication (401 response).
+    * Minimum supported version is Windows 7.
+    * https://docs.microsoft.com/en-us/security-updates
+    * /SecurityAdvisories/2009/973811
+    */
+    if(nego->sslContext) {
+      SEC_CHANNEL_BINDINGS channelBindings;
+      SecPkgContext_Bindings pkgBindings;
+      pkgBindings.Bindings = &channelBindings;
+      nego->status = s_pSecFn->QueryContextAttributes(
+          nego->sslContext,
+          SECPKG_ATTR_ENDPOINT_BINDINGS,
+          &pkgBindings
+      );
+      if(nego->status == SEC_E_OK) {
+        chlg_desc.cBuffers++;
+        chlg_buf[1].BufferType = SECBUFFER_CHANNEL_BINDINGS;
+        chlg_buf[1].cbBuffer   = pkgBindings.BindingsLength;
+        chlg_buf[1].pvBuffer   = pkgBindings.Bindings;
+      }
+    }
+#endif
   }
 
   /* Setup the response "output" security buffer */

lib/vtls/schannel.c

@@ -1428,7 +1428,7 @@ schannel_connect_common(struct connectdata *conn, int sockindex,
      * binding to pass the IIS extended protection checks.
      * Available on Windows 7 or later.
      */
-    conn->ntlm.sslContext = &BACKEND->ctxt->ctxt_handle;
+    conn->sslContext = &BACKEND->ctxt->ctxt_handle;
 #endif
 
     *done = TRUE;