Actually you say with your code that you will send url-encoded data to your server, but you are overriding the postBody of your request with custom data. So you should create your request with:
NSMutableURLRequest *request=[httpClient requestWithMethod:@"POST" path:nil parameters:loginParameters];
And you should delete below lines:
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:loginParameters options:kNilOptions error:nil];
[request setHTTPBody:jsonData];
I think above changes will be enough.