This is a step by step guide for authenticating and saving users in Django using Foursquare and OAuth without having to use a large library like django-social. This can also be used as a guide for implementing other third party applications (i.e. Instagram, Twitter, etc) as your Django authentication and user creation source. STEP ONE: Register …

backends.py

from django.contrib.auth.models import User
from django.contrib.auth.backends import ModelBackend


class FoursquareBackend(ModelBackend):
    def authenticate(self, username=None, password=None):
        try:
            user = User.objects.get(username=username)
            return user
        except User.DoesNotExist:
            print "Looks like this user does not exist"
        return None

    def get_user(self, user_id):
        try:
            return User.objects.get(pk=user_id)
        except User.DoesNotExist:
            return None

foursq_login.html

{% extends "base.html" %}

{% block title %}YOUR_APP -- Foursquare{% endblock %}

{% block body %}
    <div id="login">
	    <p>Sign in with Foursquare to begin.</p>
	    <p><a href="{% url 'foursq_auth' %}">Login</a></p>
	</div>
{% endblock %}

foursq_welcome.html

{% extends "base.html" %}

{% block title %}YOUR_APP -- Welcome{% endblock %}

{% block body %}
    <p>Hi {{ user.first_name }}, you've successfully logged in! </p>
    <a href="{% url 'foursq_unauth' %}">Logout</a>
{% endblock %}

settings.py

  ##############################
 #####     FOURSQUARE     #####
##############################

FSQ_CLIENT_ID = 'YOUR_CLIENT_ID'
FSQ_CLIENT_SECRET = 'YOUR_CLIENT_SECRET'
FSQ_ACCESS_TOKEN_URL = 'https://foursquare.com/oauth2/access_token'
FSQ_AUTHORIZE_URL = 'https://foursquare.com/oauth2/authenticate'
FSQ_REDIRECT_URL = 'YOUR_REDIRECT_URL'


AUTHENTICATION_BACKENDS = ('django.contrib.auth.backends.ModelBackend',
                           'YOUR_APP.backends.FoursquareBackend',)

urls.py

from django.conf.urls import patterns, url

from YOUR_APP import views

urlpatterns = patterns('',
    # Main is where you'll have a button to login via Foursquare
    url(r'^foursquare/$', views.foursq_main, name='foursq_main'),
    # This is your callback URL
    url(r'^foursquare/callback/$', views.foursq_callback, name='foursq_callback'),
    # This is the user logout URL
    url(r'^foursquare/logout/$', views.foursq_unauth, name='foursq_unauth'),
    # This URL calls the Foursquare authentication process
    url(r'^foursquare/auth/$', views.foursq_auth, name='foursq_auth'),
    # This URL saves the user in auth_user, authenticates and logs them in
    url(r'^foursquare/done/$', views.foursq_done, name='foursq_done'),
    # This URL is the welcome page after a user has been logged in successfully
    url(r'^foursquare/welcome/$', views.foursq_welcome, name='foursq_welcome'),
)

views.py

from django.core.urlresolvers import reverse
from django.shortcuts import redirect
from django.template.response import TemplateResponse
from django.contrib.auth.decorators import login_required
from django.contrib.auth import *
from django.contrib.auth.models import User
from django.contrib.auth import authenticate, login, logout

import urllib
import urllib2
import json

from models import *
from YOUR_PROJECT.settings import FSQ_CLIENT_ID, FSQ_CLIENT_SECRET, FSQ_ACCESS_TOKEN_URL, FSQ_AUTHORIZE_URL, FSQ_REDIRECT_URL

  ##############################
 #####     FOURSQUARE     #####
##############################


def foursq_main(request):
    return TemplateResponse(request, 'foursq_auth/foursq_login.html')


def foursq_auth(request):
    # build the url to request
    params = {'client_id': FSQ_CLIENT_ID,
              'response_type': 'code',
              'redirect_uri': FSQ_REDIRECT_URL}
    data = urllib.urlencode(params)
    # redirect the user to the url to confirm access for the app
    return redirect('%s?%s' % (FSQ_AUTHORIZE_URL, data))


def foursq_callback(request):
    # get the code returned from foursquare
    code = request.GET.get('code')

    # build the url to request the access_token
    params = {'client_id': FSQ_CLIENT_ID,
              'client_secret': FSQ_CLIENT_SECRET,
              'grant_type': 'authorization_code',
              'redirect_uri': FSQ_REDIRECT_URL,
              'code': code}
    data = urllib.urlencode(params)
    req = urllib2.Request(FSQ_ACCESS_TOKEN_URL, data)

    # request the access_token
    response = urllib2.urlopen(req)
    access_token = json.loads(response.read())
    access_token = access_token['access_token']

    # store the access_token for later use
    request.session['access_token'] = access_token

    # redirect the user to show we're done
    return redirect(reverse('foursq_done'))


def foursq_done(request):
    # get the access_token
    access_token = request.session.get('access_token')
    
    # request user details from foursquare
    params = {'oauth_token': access_token}
    data = urllib.urlencode(params)
    url = 'https://api.foursquare.com/v2/users/self'
    full_url = url + '?' + data
    response = urllib2.urlopen(full_url)
    response = response.read()
    user_data = json.loads(response)['response']['user']

    try:
        user = User.objects.get(username=user_data['contact']['email'])
    except User.DoesNotExist:
        # Save information on user
        user = User(username=user_data['contact']['email'],
                    first_name=user_data['firstName'], last_name=user_data['lastName'],
                    email=user_data['contact']['email'])
        user.set_password(access_token)
        user.save()

    user = authenticate(username=user.username, password=user.password)

    login(request, user)

    # show the page with the user's name to show they've logged in
    return redirect(reverse('foursq_welcome'))


@login_required
def foursq_welcome(request):
    user = request.user
    return TemplateResponse(request, 'foursq_auth/foursq_welcome.html', {'user': user})


def foursq_unauth(request):
    # clear any tokens and logout
    request.session.clear()
    logout(request)
    return redirect(reverse('foursq_main'))