Slack's OIDC userinfo response uses full URLs as JSON keys for namespaced claims

Slack's openid.connect.userInfo endpoint returns Slack-specific claims (e.g. https://slack.com/user_id, https://slack.com/team_id, https://slack.com/team_name, https://slack.com/team_domain) as ordinary top-level dict keys whose names happen to be full URLs. They are not nested under a slack object. Naive parsers expecting flat alphanumeric claim names miss them entirely.

When parsing Slack OIDC userinfo, read namespaced claims as payload["https://slack.com/team_id"] (full URL string as dict key), not as a nested object lookup.