API Implicit Authentication with Python

Question

I am working on an desktop inbox notifier for StackOverflow, using the API with Python.

The script I am working on first logs the user in on StackExchange, and then requests authorisation for the application.

Assuming the application has been authorised through web-browser interaction of the user. The application should be able to make requests to the API with authentication, hence it needs the access token specific to the user. This is done with the URL: https://stackexchange.com/oauth/dialog?client_id=54&scope=read_inbox&redirect_uri=https://stackexchange.com/oauth/login_success

When requesting authorisation via the web-browser the redirect is taking place and an access code is returned after a #. However, when requesting this same URL with Python (urllib2), no hash or key is returned in the response.

Why is this and how do I get it to work?

Here is my script (it's experimental) and remember: it assumes the user has already authorised the application.

#!/usr/bin/env python

import urllib
import urllib2
import cookielib
from BeautifulSoup import BeautifulSoup
from getpass import getpass    

# Define URLs
parameters = [ 'client_id=54',
               'scope=read_inbox',
               'redirect_uri=https://stackexchange.com/oauth/login_success'
             ]

dialog_url = 'https://stackexchange.com/oauth/dialog?' + '&'.join(parameters)
login_url = 'https://openid.stackexchange.com/account/login'
submit_url = 'https://openid.stackexchange.com/account/login/submit'
authentication_url = 'http://stackexchange.com/users/authenticate?openid_identifier='

# Set counter for requests:
counter = 0

# Build opener
jar = cookielib.CookieJar()
opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(jar))


def authenticate(username='', password=''):

    '''
        Authenticates to StackExchange using user-provided username and password
    '''

    # Build up headers
    user_agent = 'Mozilla/5.0 (Ubuntu; X11; Linux i686; rv:8.0) Gecko/20100101 Firefox/8.0'
    headers = {'User-Agent' : user_agent}

    # Set Data to None
    data = None

    # 1. Build up URL request with headers and data    
    request = urllib2.Request(login_url, data, headers)
    response = opener.open(request)

    # Build up POST data for authentication
    html = response.read()
    fkey = BeautifulSoup(html).findAll(attrs={'name' : 'fkey'})[0].get('value').encode()

    values = {'email' : username,
              'password' : password,
              'fkey' : fkey}

    data = urllib.urlencode(values)

    # 2. Build up URL for authentication
    request = urllib2.Request(submit_url, data, headers)
    response = opener.open(request)


    # Check if logged in
    if response.url == 'https://openid.stackexchange.com/user':
        print ' Logged in! :) '
    else:
        print ' Login failed! :( '

    # Find user ID URL    
    html = response.read()
    id_url = BeautifulSoup(html).findAll('code')[0].text.split('"')[-2].encode()


    # 3. Build up URL for OpenID authentication
    data = None
    url = authentication_url + urllib.quote_plus(id_url)
    request = urllib2.Request(url, data, headers)
    response = opener.open(request)

    # 4. Build up URL request with headers and data
    request = urllib2.Request(dialog_url, data, headers)
    response = opener.open(request)

    if '#' in response.url:
        print 'Access code provided in URL.'
    else:
        print 'No access code provided in URL.'


if __name__ == '__main__':
    username = raw_input('Enter your username: ')
    password = getpass('Enter your password: ')
    authenticate(username, password)

Answer 1

The token does not appear because of the way urllib2 handles the redirect. I am not familiar with the details so I won't elaborate here.

The solution is to catch the 302 before urllib2 handles the redirect. This can be done by sub-classing the urllib2.HTTPRedirectHandler to get the redirect with its hash and token.
Here is a short example of subclassing the handler:

class MyHTTPRedirectHandler(urllib2.HTTPRedirectHandler):
    def http_error_302(self, req, fp, code, msg, headers):
        print "Going through 302:\n"
        print headers
        return urllib2.HTTPRedirectHandler.http_error_302(self, req, fp, code, msg, headers)

In the headers the location attribute will provide the redirect URL in full length, i.e. including the hash and token:

Output extract:

...
Going through 302:

Server: nginx/0.7.65
Date: Mon, 09 Jan 2012 20:20:11 GMT
Content-Type: text/html; charset=utf-8
Connection: close
Cache-Control: private
Location: https://stackexchange.com/oauth/login_success#access_token=K4zKd*HkKw5Opx(a8t12FA))&expires=86400
Content-Length: 218
...

More on catching redirects with urllib2 on Stack Overflow (of course).