pub fn subject(contact: Option<&str>, public_url: &PublicUrl) -> Option<String>Expand description
A VAPID token’s sub (kernel spec §6; maintainer decision 6b): mailto:
the owner’s contact (contact_problem keeps it free of anything mailto:
would need escaped), else the public_url origin when it is https.
None for an http one (loopback): kernel §6 never sends a
non-routable sub, and Apple refuses anything but mailto: or https:
(the review’s N1), so the token carries none.