title: Kivy UrlRequest not passing data
body: <p>I am writing a flask backend with flask sqlalchemy and marshmallow which returns json and kivy as frontend. I am trying to login in my flask api using kivy urlrequest but no data is been passed. I get error from my flask api ('no input data provided') even so i passed valid data.</p>
  
  <pre><code>from kivy.network.urlrequest import UrlRequest
  import urllib
  import json
  
  def success(req, result):
      print('success')
  
  def fail(req, result):
      print('fail')
  
  def error(req, result):
      print('error')
  
  def progress(req, result, chunk):
      print('loading')
  
  values = {'email':'wilson@gmail.com', 'pwdhash':'wilson'}
  params = urllib.urlencode(values)
  headers = {'Content-type': 'application/x-www-form-urlencoded',
            'Accept': 'text/plain'}
  
  req = UrlRequest('http://127.0.0.1:5000/login', on_success=success, on_failure=fail, on_error=error, on_progress=progress, req_body=params, req_headers=headers)
  req.wait()
  print(req.result)
  </code></pre>
  
  <p>please how to fix this?</p>