Restore default HTML redirect on facebook app backend

social_auth/backends/facebook.py

@@ -1,8 +1,41 @@
 from django.conf import settings
+from django.template import TemplateDoesNotExist
 
 
-# TODO: review HTML rendering in facebook app backend
 if getattr(settings, 'FACEBOOK_APP_AUTH', False):
-    from social.backends.facebook import FacebookAppOAuth2 as FacebookBackend
+    from social.backends.facebook import \
+            FacebookAppOAuth2 as FacebookBackendBase
 else:
-    from social.backends.facebook import FacebookOAuth2 as FacebookBackend
+    from social.backends.facebook import FacebookOAuth2 as FacebookBackendBase
+
+
+REDIRECT_HTML = """
+<script type="text/javascript">
+    var domain = 'https://apps.facebook.com/',
+        redirectURI = domain + '{{ FACEBOOK_APP_NAMESPACE }}' + '/';
+    window.top.location = 'https://www.facebook.com/dialog/oauth/' +
+    '?client_id={{ FACEBOOK_KEY }}' +
+    '&redirect_uri=' + encodeURIComponent(redirectURI) +
+    '&scope={{ FACEBOOK_EXTENDED_PERMISSIONS }}';
+</script>
+"""
+
+
+class FacebookBackend(FacebookBackendBase):
+    def auth_html(self):
+        key, secret = self.get_key_and_secret()
+        namespace = self.setting('NAMESPACE', None)
+        scope = self.get_scope()
+        if scope:
+            scope = self.SCOPE_SEPARATOR.join(scope)
+        ctx = {
+            'FACEBOOK_APP_NAMESPACE': namespace or key,
+            'FACEBOOK_KEY': key,
+            'FACEBOOK_EXTENDED_PERMISSIONS': scope,
+            'FACEBOOK_COMPLETE_URI': self.redirect_uri,
+        }
+        tpl = self.setting('LOCAL_HTML', 'facebook.html')
+        try:
+            return self.strategy.render_html(tpl=tpl, context=ctx)
+        except TemplateDoesNotExist:
+            return self.strategy.render_html(html=REDIRECT_HTML, context=ctx)