Added backend for Last.Fm. There is probably an easier way to impleme…

…nt this.

social/backends/lastfm.py

@@ -0,0 +1,74 @@
+from social.backends.base import BaseAuth
+from social.backends.oauth import BaseOAuth1
+from social.exceptions import AuthException
+import hashlib
+import json
+import logging
+import urllib
+
+class LastFmAuth(BaseAuth):
+    """Last.Fm authentication backend. Requires two settings: LASTFM_API_KEY and LASTFM_SECRET.
+    Don't forget to set the Last.fm callback to something sensible (http://your.site/lastfm/complete)."""
+    # Similar to OAuth.
+    # 1. Server redirects user to http://www.last.fm/api/auth with the api key (LASTFM_API_KEY).
+    # 2. Last.fm asks user to authorize. If user agrees, user is redirected to a callback url (/lastfm/complete) with a temporary token.
+    # 3. Server builds a signed request using the temporary token and sends it to Last.fm.
+    # 4. Last.fm responds with a username and session key.
+    # 5. User is logged in.
+    #    The session key can be used by the server to make signed requests on behalf of the user.
+
+    name = "lastfm"
+    EXTRA_DATA = [
+        ('key', 'session_key')
+    ]
+
+    def auth_url(self):
+        return "http://www.last.fm/api/auth/?api_key={api_key}".format(api_key=self.setting('LASTFM_API_KEY'))
+
+    def auth_complete(self, *args, **kwargs):
+        """Completes login process, must return user instance"""
+
+        # Sign session request.
+        signature_base = "api_key{api_key}methodauth.getSessiontoken{token}{secret}".format(
+            api_key=self.setting('LASTFM_API_KEY'),
+            token=self.data['token'],
+            #secret=settings.LASTFM_SECRET,
+            secret=self.setting('LASTFM_SECRET'),
+        )
+        signature = hashlib.md5(signature_base).hexdigest()
+        logging.debug("Generated signature {signature} from {signature_base}".format(signature=signature, signature_base=signature_base))
+
+        session_key_request_template = "http://ws.audioscrobbler.com/2.0/?method=auth.getSession&api_key={api_key}&token={token}&api_sig={api_sig}&format=json"
+        session_key_request = session_key_request_template.format(
+            api_key=self.setting('LASTFM_API_KEY'),
+            token=self.data['token'],
+            api_sig=signature,
+        )
+        urlopener = urllib.FancyURLopener()
+        logging.debug("Requesting session key for token {token} using signature {signature}".format(token=self.data['token'], signature=signature))
+        # {"session":{"name":"xxxxxxxx","key":"xxxxxxxxx","subscriber":"0"}}
+        session_request_response = urlopener.open(session_key_request, signature).read()
+        logging.debug("Last.fm responded with {response} for session key request {request}".format(
+            response=session_request_response,
+            request=session_key_request,
+        ))
+
+        kwargs.update({'response': json.loads(session_request_response)['session'], 'backend': self})
+        return self.strategy.authenticate(*args, **kwargs)
+
+    def get_user_id(self, details, response):
+        """Return a unique ID for the current user, by default from server
+        response."""
+        return response.get('name')
+
+    def get_user_details(self, response):
+        """
+        """
+        return {
+            'username': response['name'],
+            'email': '',
+            'fullname': response['name'],
+            'first_name': '',
+            'last_name': '',
+        }
+