Getting an Ebay OAuth Token

I've been working on the ebaySDK for most of the week. I've managed to integrate the Trading and Shopping APIs into my project. For the trading API, I was using an Auth n Auth token which has a validity of upto 18 months. The OAuth Token which I need for the Sell APIs is valid only for a day, so I'll need to fetch it regularly before it expires. I followed the documentation on the site and even tried looking through python repos on github but I haven't been able to move forward as of yet. Here's a quick snippet of my request code, What am I doing wrong?

import requests, json, base64, xmltodict

AppSettings = {
    'app_id' : 'my_app_id',
    'app_secret' : 'my_app_secret',
    'dev_id': 'my_dev_id',
    'ruName': 'the_ruName_for_my_app'
}
authHeaderData =  AppSettings['app_id']+':'+AppSettings['app_secret']
encodedAuthHeader = base64.b64encode(authHeaderData)

session = requests.Session()

print encodedAuthHeader 
url = 'https://api.ebay.com/identity/v1/oauth2/token'

session.headers.update({
    'Content-Type':'application/x-www-form-urlencoded',
    'Authorization':'Basic '+encodedAuthHeader
    })

data = {
    'grant_type':'client_credentials',
    'redirect_uri': AppSettings['ruName'],
    'scope':'https://api.ebay.com/oauth/api_scope'
}

response = session.post(url, data=data).json()
print response

The response I'm getting is:

{u'error_description': u'client authentication failed', u'error': u'invalid_client'}

I checked all the keys. I even tried to get the token via the production signin provided by ebay but to no avail. The response I got from the url provided by ebay was html and js code (No JSON or any data).

Has anybody faced a similar issue? How can I work through this? Am I making the requests wrong? Any insight is greatly appreciated

Because this was such a nightmare to traverse eBays docs to find this answer, I figured i would post my function that solved this.

import requests, urllib, base64

def getAuthToken():
     AppSettings = {
          'client_id':'<client_id>',
          'client_secret':'<client_secret>',
          'ruName':'<ruName>'}

     authHeaderData = AppSettings['client_id'] + ':' + AppSettings['client_secret']
     encodedAuthHeader = base64.b64encode(str.encode(authHeaderData))

     headers = {
          "Content-Type" : "application/x-www-form-urlencoded", 
          "Authorization" : "Basic " + str(encodedAuthHeader)
          }

     body= {
          "grant_type" : "client_credentials",
          "redirect_uri" : AppSettings['ruName'],
          "scope" : "https://api.ebay.com/oauth/api_scope"
      }

     data = urllib.parse.urlencode(body)

     tokenURL = "https://api.ebay.com/identity/v1/oauth2/token"

     response = requests.post(tokenURL, headers=headers, data=data) 
     return response.json()


response = getAuthToken()
print(response)
response['access_token'] #access keys as required
response['error_description'] #if errors