migrate from urllib2 to requests python 2.7 - python-2.7

Question

I am trying to take some working code and change from urlib2 to requests.
The original code provides basic login information of username, password and posts the KEY and SECRET in the header of the urllib2 request. The following code is my attempt to change to using the requests module and gain some functionality for making additional API calls. I have tried dozens of combinations and all return a code 400. Apparently, my requests code does not successfully furnish the needed information to return a 200 response and provide the needed authorization token.
## Import needed modules
import urllib2, urllib, base64
import httplib
import requests
import json
## initialize variables
KEY = "7f1xxxx-3xxx-4xxx-9a7f-8be66839dede"
SECRET = "45xxxxxx-45xxx-469a-9ae9-a7927a76cfeb"
userName = "my-email#xxx.com"
passWord = "mypassword"
URL = "https://company.com/auth/token"
token = None
sessionid = None
DATA = urllib.urlencode({"grant_type":"password",
"username":userName,
"password":passWord})
base64string = base64.encodestring('%s:%s' % (KEY, SECRET)).replace('\n', '')
request = urllib2.Request(URL, DATA)
request.add_header("Authorization", "Basic %s" % base64string)
result = urllib2.urlopen(request)
token = result.read()
print token
This returns my authorization token and all is well. I can pass the token to the authorization server and have full access to the api for interacting with the database. Below is the attempt to use requests and have the added functions it provides.
client = requests.session()
payload = {"grant_type":"password",
"username":userName,
"password":passWord,
"applicationId": KEY
}
headers = {'content-type':'application/json',
"grant_type":"password",
"username":userName,
"password":passWord,
'applicationsId': KEY,
'Authorization': base64string,
'token': token,
'sessionid': sessionid
}
response = client.post(URL, params = payload, headers=headers)
token = response.content
print token
{"error":"invalid_request"}
print response
<Response [400]>

Answer 1

If you want to use basic auth you should use the method from requests..
Your post should look like
response = client.post(
URL,
params = payload,
headers=headers,
auth=HTTPBasicAuth(
KEY,
SECRET
))

Answer 2

Somewhere in a post a contributor to another question mentioned some items actually needed to be in the body of the request not in the header. I tried various combos and the following solved the 400 response and accomplished my goals.
data = {"grant_type":"password",
"username":userName,
"password":passWord,
"applicationId": KEY
}
headers = {'Authorization': "Basic %s" % base64string,
'token': token
}
response = client.post(URL, data = data, headers=headers)
token = response.text
print token