Add option to pass kc_idp_hint

This is currently not working, but can be used later

config/auth.py

@@ -35,9 +35,18 @@ def get_user(self, user_id: Any = None) -> User | None:
 
     def auth_params(self, state: str | None = None) -> dict[str, str]:
         params = super().auth_params(state)
-        lang = self.strategy.request_data().get("ui_locales")
+
+        request_data = self.strategy.request_data()
+
+        # Parameters from `tilavarauspalvelu.api.helauth.views.login_view`.
+        lang = request_data.get("ui_locales")
+        login_method_hint = request_data.get("kc_idp_hint")
+
         if lang:
             params["ui_locales"] = lang
+        if login_method_hint:
+            params["kc_idp_hint"] = login_method_hint
+
         return params
 
     def get_end_session_url(self, request: WSGIRequest, id_token: str) -> str | None:

tilavarauspalvelu/api/helauth/views.py

@@ -31,6 +31,11 @@ def login_view(request: WSGIRequest) -> HttpResponseRedirect:
     if lang:
         url = update_query_params(url, ui_locales=lang)
 
+    login_method_hint: str | None = request.GET.get("ui")
+    if login_method_hint == "customer":
+        # For `kc_idp_hint`, see: https://www.keycloak.org/docs/latest/server_admin/#_client_suggested_idp
+        url = update_query_params(url, kc_idp_hint="suomi_fi")
+
     return HttpResponseRedirect(url)