Paginating through lists - "error": "Couldn't authenticate you"

I'm trying to get a list of users through the API and even using the exact code from the documentation its not working. I'm using Python to make the request and when I run this code 

while url:
    response = requests.get(url, auth=auth, params=params)
    data = response.json()

    # do something with the data
    for user in data['users']:
        print(user['name'])

    if data['meta']['has_more']:
        params['page[after]'] = data['meta']['after_cursor']
    else:
        url = None

I get 'error': "Couldn't authenticate you".

It only breaks when it's in the loop, if I try to pull a single page outside the loop it works no issue, but if I try to loop it I get nothing.  

Any assistance with this error is appreciated.