Function validate_vapid_jwt

fn validate_vapid_jwt(
    vapid: &VapidHeaderWithKey,
    settings: &Settings,
    metrics: &Metrics,
) -> Result<(), ApiError>

Validate the VAPID JWT token. Specifically,

• Check the signature
• Make sure it hasn’t expired
• Make sure the expiration isn’t too far into the future

This is mostly taken care of by the jsonwebtoken library