✅(backend) handle inactive user

Handle case where user is inactive.
Previously this edge case would cause unexpected behavior.

Related to previous commit that added the test coverage.

src/backend/core/authentication/backends.py

@@ -83,4 +83,10 @@ class OIDCAuthenticationBackend(MozillaOIDCAuthenticationBackend):
             else:
                 user = None
 
+        if not user:
+            return None
+
+        if not user.is_active:
+            raise SuspiciousOperation(_("User account is disabled"))
+
         return user