Fix #1054

httplib.h

@@ -4074,11 +4074,14 @@ inline std::pair<std::string, std::string> make_digest_authentication_header(
     }
   }
 
-  auto field = "Digest username=\"" + username + "\", realm=\"" +
-               auth.at("realm") + "\", nonce=\"" + auth.at("nonce") +
-               "\", uri=\"" + req.path + "\", algorithm=" + algo +
-               ", qop=" + qop + ", nc=\"" + nc + "\", cnonce=\"" + cnonce +
-               "\", response=\"" + response + "\"";
+  auto field =
+      "Digest username=\"" + username + "\", realm=\"" + auth.at("realm") +
+      "\", nonce=\"" + auth.at("nonce") + "\", uri=\"" + req.path +
+      "\", algorithm=" + algo +
+      (qop.empty() ? ", response=\""
+                   : ", qop=" + qop + ", nc=\"" + nc + "\", cnonce=\"" +
+                         cnonce + "\", response=\"") +
+      response + "\"";
 
   auto key = is_proxy ? "Proxy-Authorization" : "Authorization";
   return std::make_pair(key, field);