static  TCHttpRequest *_sharedHttpRequest = nil;
+ (id)sharedRequest
{
    @synchronized(self){
        if (_sharedHttpRequest == nil) {
            _sharedHttpRequest = [[self alloc] init];
        }
    }
    return  _sharedHttpRequest;
}


- (NSDictionary *)loginWithUserName:(NSString *)user password:(NSString *)pwd
{
    NSURL *url = [NSURL URLWithString:@"/login" relativeToURL:_url];

    ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:url];
    [request setCachePolicy:ASICacheForSessionDurationCacheStoragePolicy];
    [request setTimeOutSeconds:HTTP_REQ_TIMEOUT];
    [request addPostValue:user forKey:@"username"];
    [request addPostValue:pwd forKey:@"password"];
    request.delegate = self.delegate;
    [_common_queue addOperation:request];
}