@Override
        public byte[] getBody() throws AuthFailureError {
            String httpPostBody="grant_type=password&username=Alice&password=password123";
            // usually you'd have a field with some values you'd want to escape, you need to do it yourself if overriding getBody. here's how you do it
            try {
                httpPostBody=httpPostBody+"&randomFieldFilledWithAwkwardCharacters="+URLEncoder.encode("{{%stuffToBe Escaped/","UTF-8");
            } catch (UnsupportedEncodingException exception) {
                Log.e("ERROR", "exception", exception);
                // return null and don't pass any POST string if you encounter encoding error
                return null;
            }
            return httpPostBody.getBytes();
        }