Add config option to toggle dns case randomization.

Signed-off-by: Jason Volk <jason@zemos.net>

tuwunel-example.toml

@@ -302,6 +302,18 @@
 #
 #dns_passthru_appservices = false
 
+# Enable or disable case randomization for DNS queries. This is a security
+# mitigation where answer spoofing is prevented by having to exactly match
+# the question. Occasional errors seen in logs which may have lead you
+# here tend to be from overloading DNS. Nevertheless for servers which
+# are truly incapable this can be set to false.
+#
+# This currently defaults to false due to user reports regarding some
+# popular DNS caches which may or may not be patched soon. It may again
+# default to true in an upcoming release.
+#
+#dns_case_randomization = false
+
 # Max request size for file uploads in bytes. Defaults to 20MB.
 #
 #max_request_size = 20971520