support alternative cookie messages in UI (iss. #107) (#109)

* #107 - support alternative messages

This could be used as…

```python
    path("init/<uuid:registration_uuid>/", OIDCLoginInitView.as_view(
        main_msg='Your browser prevents embedded content from using cookies.',
        click_msg='Instead, you must open the content in a new tab.',
        loading_msg='Loading…'
    ), name="init"),
```

* #107 - nox/black formatting and comments

After running `nox`, `black` said a blank line was needed.  After I looked, I decided a comment would be helpful, too.

* #107 - set better default message values

* #107 - document optional message arguments

* added common `virtualenv` direcory name, `.venv`

* #109 - clean up code

* #109 - keep old example; add cookie lang. example

docs/oidc_initiation.rst

@@ -16,19 +16,52 @@ to return an authentication request to the platform
 
 .. code-block:: python
 
-    ...
-
+    # ...
     from lti_tool.views import OIDCLoginInitView
 
     urlpatterns = [
         path("init/<uuid:registration_uuid/", OIDCLoginInitView.as_view(), name="init"),
-        ...
+        # ...
     ]
 
 The ``registration_uuid`` parameter is a reference to the
 :attr:`LtiRegistration.uuid <lti_tool.models.LtiRegistration.uuid>` property, and is
 used to identify the platform registration associated with the initiation request.
 
+
+Customizing language for blocked cookies
+----------------------------------------
+
+When the user's browser prevents embedded content from setting cookies within an
+``iframe``, the module displays a message about it and a link to open the
+content in a new tab or window.  The language of the message and link may be
+customized using optional message arguments to ``OIDCLoginInitView.as_view()``…
+
+.. code-block:: python
+
+    # ...
+    from lti_tool.views import OIDCLoginInitView
+
+    urlpatterns = [
+        path("init/<uuid:registration_uuid/", OIDCLoginInitView.as_view(
+            main_msg=(
+                "Your browser prevents embedded content from using cookies.  To work "
+                "around this, the content must be opened in a new tab or window.  "
+            ),
+            click_msg="Open a new tab or window now.",
+            loading_msg="Loading..."
+        ), name="init"),
+        # ...
+    ]
+
+The ``main_msg``, ``click_msg``, and ``loading_msg`` **optional** arguments are
+passed to ``DjangoOIDCLogin.enable_check_cookies()`` to generate messages shown
+in the UI.  The values shown here are the default values used by
+``OIDCLoginInitView``.  If cookies are not allowed by the browser, the value of
+``main_msg`` will be shown.  That will be followed by a link with label
+containing the value of ``click_msg``, which opens the content in a new tab or
+window.
+
 Customizing the authentication request
 --------------------------------------
 

lti_tool/views.py

@@ -30,6 +30,13 @@ def jwks(request):
 class OIDCLoginInitView(View):
     """Handles OIDC 3rd-party login initiation for an LTI launch."""
 
+    main_msg = (
+        "Your browser prevents embedded content from using cookies.  To work "
+        "around this, the content must be opened in a new tab or window.  "
+    )
+    click_msg = "Open a new tab or window now."
+    loading_msg = "Loading..."
+
     def get(self, request, *args, **kwargs):
         registration_uuid = kwargs.get("registration_uuid")
         return self.get_oidc_response(request, registration_uuid, request.GET)
@@ -52,7 +59,9 @@ def get_oidc_response(self, request, registration_uuid, params):
         if target_link_uri is None:
             return HttpResponseBadRequest("Missing target_link_uri parameter.")
         redirect_url = self.get_redirect_url(target_link_uri)
-        return oidc_login.enable_check_cookies().redirect(redirect_url)
+        return oidc_login.enable_check_cookies(
+            self.main_msg, self.click_msg, self.loading_msg
+        ).redirect(redirect_url)
 
 
 @method_decorator(csrf_exempt, name="dispatch")

setup.cfg

@@ -50,4 +50,4 @@ extend-ignore =
   D105,  # Missing docstring in magic method
   D106,  # Missing docstring in public nested class
   D107,  # Missing docstring in __init__
-exclude = build/*, env/*, venv/*, .nox, lti_tool/migrations/*
+exclude = build/*, env/*, venv/*, .venv/*, .nox, lti_tool/migrations/*