🚸(oidc) ignore case when fallback on email

Some identity providers might change the case, but in our
products we don't consider case variation to be consider as
different email addresses.

Next step would be to normalize the DB value of email to
be lower-case.

tests/oidc_login/test_backends.py

@@ -162,6 +162,25 @@ def test_authentication_getter_existing_user_via_email(django_assert_num_queries
     assert user == db_user
 
 
+def test_authentication_getter_existing_user_via_email_case(django_assert_num_queries, monkeypatch):
+    """
+    If an existing user doesn't match the sub but matches the email with different case,
+    the user should be returned.
+    """
+    klass = OIDCAuthenticationBackend()
+    db_user = factories.UserFactory(email="Some.User@example.com")
+
+    def get_userinfo_mocked(*args):
+        return {"sub": "123", "email": "sOmE.useR@example.com"}
+
+    monkeypatch.setattr(OIDCAuthenticationBackend, "get_userinfo", get_userinfo_mocked)
+
+    with django_assert_num_queries(3):  # user by email + user by sub + update sub
+        user = klass.get_or_create_user(access_token="test-token", id_token=None, payload=None)
+
+    assert user == db_user
+
+
 def test_authentication_getter_existing_user_no_fallback_to_email(settings, monkeypatch):
     """
     When the "OIDC_FALLBACK_TO_EMAIL_FOR_IDENTIFICATION" setting is set to False,