always 403 forbiden for json package,@csrf_exempt do not wrok

[thinksource]

Hi, I want to send an ajax request: by $.post
javascript code：
data='{"jsonrpc": "2.0", "method": "secret", "params": {"a": "as12"}, "id": 1}'
$.post(
'RPC2',
data,
function(data1) {
alert("Response: " + data1);
}
);

the python receive code:
@csrf_exempt
@jsonrpc_method('app.addStrings(arg1=String) -> String', validate=True)
def add(request, secret_data):

print request.COOKIES
print request.body
re=request.REQUEST
print repr(re)

result=0;
for k in re:
    print "dict[%s] =" % k,re[k]
rep = re.get('params', None)
print rep
return HttpResponse(json.dumps({'message':'Hello World'}), content_type="application/json")

but I get the 403 Forbiden as CSRF problem.
I think I have already writen @csrf_exempt, but it don't work.