- Internet Explorer had a broken HTTP digest authentication before v7 and

there are servers "out there" that relies on the client doing this broken
  Digest authentication. Apache even comes with an option to work with such
  broken clients.

  The difference is only for URLs that contain a query-part (a '?'-letter and
  text to the right of it).

  libcurl now supports this quirk, and you enable it by setting the
  CURLAUTH_DIGEST_IE bit in the bitmask you pass to the CURLOPT_HTTPAUTH or
  CURLOPT_PROXYAUTH options. They are thus individually controlled to server
  and proxy.

include/curl/curl.h

@@ -474,8 +474,9 @@ typedef enum {
 #define CURLAUTH_DIGEST       (1<<1)  /* Digest */
 #define CURLAUTH_GSSNEGOTIATE (1<<2)  /* GSS-Negotiate */
 #define CURLAUTH_NTLM         (1<<3)  /* NTLM */
-#define CURLAUTH_ANY ~0               /* all types set */
-#define CURLAUTH_ANYSAFE (~CURLAUTH_BASIC)
+#define CURLAUTH_DIGEST_IE    (1<<4)  /* Digest with IE flavour */
+#define CURLAUTH_ANY (~CURLAUTH_DIGEST_IE)  /* all fine types set */
+#define CURLAUTH_ANYSAFE (~(CURLAUTH_BASIC|CURLAUTH_DIGEST_IE))
 
 #define CURLSSH_AUTH_ANY       ~0     /* all types supported by the server */
 #define CURLSSH_AUTH_NONE      0      /* none allowed, silly but complete */