misc: allow login_hint parameter in login url (#76712)

mellon/utils.py

@@ -357,3 +357,13 @@ def is_slo_supported(request, issuer):
         server.getFirstHttpMethod(server.providers[issuer], lasso.MD_PROTOCOL_TYPE_SINGLE_LOGOUT)
         != lasso.HTTP_METHOD_NONE
     )
+
+
+def get_login_hints_from_request(request):
+    request_login_hints = request.GET.getlist('login_hint')
+    login_hints = [
+        login_hint.strip()
+        for login_hint in request_login_hints
+        if login_hint.isascii() and login_hint.isprintable()
+    ]
+    return login_hints

mellon/views.py

@@ -591,13 +591,16 @@ class LoginView(ProfileMixin, LogMixin, View):
 
     def add_login_hints(self, idp, authn_request, request, next_url=None):
         login_hints = utils.get_setting(idp, 'LOGIN_HINTS', [])
-        hints = []
+        hints = set()
         for login_hint in login_hints:
             if login_hint == 'backoffice':
                 if next_url and self.is_in_backoffice(request, next_url):
-                    hints.append('backoffice')
+                    hints.add('backoffice')
             if login_hint == 'always_backoffice':
-                hints.append('backoffice')
+                hints.add('backoffice')
+
+        for login_hint in utils.get_login_hints_from_request(request):
+            hints.add(login_hint)
 
         for hint in hints:
             node = ET.Element(LOGIN_HINT)

tests/test_sso_slo.py

@@ -922,3 +922,12 @@ def test_sso_slo_update_of_new_fields(db, app, idp, caplog, sp_settings):
     caplog.clear()
     response = app.get(url)
     assert len(caplog.records) == 0, 'logout failed'
+
+
+def test_sso_slo_pass_login_hints_from_request(db, app, idp, caplog, sp_settings):
+    response = app.get(reverse('mellon_login') + '?next=/whatever/&login_hint=azure')
+    url, body, relay_state = idp.process_authn_request_redirect(response['Location'])
+    root = ET.fromstring(idp.request)
+    login_hints = root.findall('.//{https://www.entrouvert.com/}login-hint')
+    assert len(login_hints) == 1, 'missing login hint'
+    assert login_hints[0].text == 'azure', 'login hint is not azure'