utils: add method to check if a user has a role

Along with a middleware to allow catching the exception it raises when
the user is missing roles, redirecting them appropriately.

A distinction is made between roles which are obtained at the SSO,
stored in session, and roles which the user could have, statically
stored in database.

todo: ce commit dépend totalement du provisionning tel qu'implémenté par
hobo, il faudrait améliorer ça

mellon/exceptions.py

@@ -0,0 +1,4 @@
+class RolesNotInSession(Exception):
+
+    def __init__(self, roles):
+        self.roles = roles

mellon/middleware.py

@@ -3,6 +3,7 @@ from django.http import HttpResponseRedirect
 from django.core.urlresolvers import reverse
 
 from . import app_settings, utils
+from .exceptions import RolesNotInSession
 
 PASSIVE_TRIED_COOKIE = 'MELLON_PASSIVE_TRIED'
 
@@ -50,3 +51,10 @@ class PassiveAuthenticationMiddleware(object):
             # prevent loops
             response.set_cookie(PASSIVE_TRIED_COOKIE, value='1', max_age=None)
             return response
+
+
+class RolesRequestMiddleware(object):
+    def process_exception(self, request, exception):
+        if isinstance(exception, RolesNotInSession):
+            return HttpResponseRedirect(
+                utils.get_role_request_url(request, exception.roles))

mellon/utils.py

@@ -6,7 +6,9 @@ import isodate
 from xml.parsers import expat
 
 from django.contrib import auth
+from django.contrib.auth.models import Group
 from django.core.urlresolvers import reverse
+from django.http import QueryDict, HttpResponseRedirect
 from django.template.loader import render_to_string
 from django.utils.timezone import make_aware, now, make_naive, is_aware, get_default_timezone
 from django.conf import settings
@@ -14,6 +16,7 @@ from django.utils.six.moves.urllib.parse import urlparse
 import lasso
 
 from . import app_settings
+from .exceptions import RolesNotInSession
 
 
 def create_metadata(request):
@@ -289,3 +292,31 @@ def has_superuser_flag(idp, saml_attributes):
             if attribute_values & values:
                 return True
     return False
+
+
+def user_has_roles(request, roles):
+    if request.user.is_staff and request.session.get('is_staff'):
+        return True
+    groups = set(roles).intersection(request.user.groups.all())
+    if not groups:
+        if request.user.is_staff:
+            raise RolesNotInSession(('staff',))
+        return False
+    role_uuids = {getattr(group, 'role').uuid for group in groups}
+    if not role_uuids:
+        return True
+    if set(request.session['mellon_session']['role-slug']) & role_uuids:
+        return True
+    raise RolesNotInSession(role_uuids)
+
+
+def user_has_role(request, role):
+    return user_has_roles(request, {role})
+
+
+def get_role_request_url(request, roles):
+    login_url = reverse(app_settings.LOGIN_URL)
+    q = QueryDict(mutable=True)
+    q.setlist('roles', roles)
+    q['next'] = request.get_full_path()
+    return '?'.join((login_url, q.urlencode(safe='/')))