Ability to handle validation logic for users

.gitignore

@@ -5,3 +5,4 @@ dist/
 *.egg-info
 .tox/
 .cache/
+*.swp

README.md

@@ -54,6 +54,9 @@ Step 6: Set up all the correct options (see below for available options)
  * OAUTHADMIN_GET_USER: This is function that is given the oauth token and returns
    a django.auth.models.User model corresponding to the currently logged-in user.
    You can set permissions on this user object and stuff.
+ * OAUTHADMIN_GET_USER_EXCEPTION_HANDLER: Callable that receives request object, OAuth token
+   and exception to handle business logics such as unauthorized users. This callable should
+   return proper response object.
  * OAUTHADMIN_CLIENT_ID: Your oAuth client ID
  * OAUTHADMIN_CLIENT_SECRET: oAuth client secret
  * OAUTHADMIN_BASE_URL: The landing point for all oAuth related queries.

oauthadmin/errors.py

@@ -0,0 +1,6 @@
+class OAuthAdminException(Exception):
+    pass
+
+
+class GetUserException(OAuthAdminException):
+    pass

oauthadmin/views.py

@@ -11,12 +11,14 @@
     from urllib.parse import quote_plus
 
 from django.shortcuts import redirect
-from django.http import HttpResponseRedirect
+from django.http import HttpResponse, HttpResponseRedirect
 
-from oauthadmin.utils import import_by_path
-from oauthadmin.settings import app_setting
 import oauthadmin.views
 
+from oauthadmin.errors import GetUserException
+from oauthadmin.settings import app_setting
+from oauthadmin.utils import import_by_path
+
 try:
     from django.urls import reverse, NoReverseMatch
 except ImportError:
@@ -82,7 +84,15 @@ def callback(request):
     except (MismatchingStateError, InvalidGrantError):
         return HttpResponseRedirect(request.build_absolute_uri(reverse(oauthadmin.views.login)))
 
-    user = import_by_path(app_setting('GET_USER'))(token)
+    user_getter = import_by_path(app_setting('GET_USER'))
+    try:
+        user = user_getter(token)
+    except GetUserException as e:
+        get_user_exception_handler_module = app_setting('GET_USER_EXCEPTION_HANDLER')
+        if get_user_exception_handler_module:
+            get_user_exception_handler = import_by_path(get_user_exception_handler_module)
+            return get_user_exception_handler(request, token, e)
+        raise
 
     request.session['last_verified_at'] = int(time())
     request.session['oauth_token'] = token