refactor: migrate THIRD_PARTY_AUTH_HINT off FEATURES-as-dict

The tpa_hint was only read via settings.FEATURES.get with an inline ''
default and was never defined in a common envs file. Add an annotated flat
setting (default '') to openedx/envs/common.py so the shared reader in
common/djangoapps/student/helpers.py can read it directly from both LMS
and CMS, and convert the test overrides.

Author: feanil

common/djangoapps/student/helpers.py

@@ -316,7 +316,7 @@ def get_next_url_for_login_page(request, include_host=False):
     # Append a tpa_hint query parameter, if one is configured
     tpa_hint = configuration_helpers.get_value(
         "THIRD_PARTY_AUTH_HINT",
-        settings.FEATURES.get("THIRD_PARTY_AUTH_HINT", '')
+        settings.THIRD_PARTY_AUTH_HINT
     )
     if tpa_hint:
         # Don't add tpa_hint if we're already in the TPA pipeline (prevent infinite loop),

common/djangoapps/student/tests/test_helpers.py

@@ -126,7 +126,7 @@ def validate_login():
             next_page = get_next_url_for_login_page(req)
             assert next_page == expected_url
 
-        with override_settings(FEATURES=dict(settings.FEATURES, THIRD_PARTY_AUTH_HINT=tpa_hint)):
+        with override_settings(THIRD_PARTY_AUTH_HINT=tpa_hint):
             validate_login()
 
         with with_site_configuration_context(configuration=dict(THIRD_PARTY_AUTH_HINT=tpa_hint)):

openedx/core/djangoapps/user_authn/views/tests/test_logistration.py

@@ -289,14 +289,14 @@ def test_hinted_login_dialog_disabled(self, url_name, auth_entry):
             target_status_code=302
         )
 
-    @override_settings(FEATURES=dict(settings.FEATURES, THIRD_PARTY_AUTH_HINT='oa2-google-oauth2'))
+    @override_settings(THIRD_PARTY_AUTH_HINT='oa2-google-oauth2')
     @ddt.data(
         'signin_user',
         'register_user',
     )
     def test_settings_tpa_hinted_login(self, url_name):
         """
-        Ensure that settings.FEATURES['THIRD_PARTY_AUTH_HINT'] can set third_party_auth_hint.
+        Ensure that settings.THIRD_PARTY_AUTH_HINT can set third_party_auth_hint.
         """
         params = [("next", "/courses/something/")]
         response = self.client.get(reverse(url_name), params, HTTP_ACCEPT="text/html")
@@ -314,7 +314,7 @@ def test_settings_tpa_hinted_login(self, url_name):
         response = self.client.get(reverse(url_name), params, HTTP_ACCEPT="text/html")
         assert response.content.decode('utf-8') not in tpa_hint
 
-    @override_settings(FEATURES=dict(settings.FEATURES, THIRD_PARTY_AUTH_HINT='oa2-google-oauth2'))
+    @override_settings(THIRD_PARTY_AUTH_HINT='oa2-google-oauth2')
     @ddt.data(
         ('signin_user', 'login'),
         ('register_user', 'register'),

openedx/envs/common.py

@@ -1166,6 +1166,12 @@ def add_optional_apps(optional_apps, installed_apps):
 # .. toggle_tickets: https://github.com/openedx/edx-platform/pull/7315
 LICENSING = False
 
+# .. setting_name: THIRD_PARTY_AUTH_HINT
+# .. setting_default: ''
+# .. setting_description: Default third-party auth provider hint (tpa_hint) to append to login/registration
+#   redirect URLs site-wide. Usually left empty and overridden per-site via site configuration.
+THIRD_PARTY_AUTH_HINT = ''
+
 # .. toggle_name: CERTIFICATES_HTML_VIEW
 # .. toggle_implementation: DjangoSetting
 # .. toggle_default: False