This commit adds a default OpenID Connect expiry to 180d to align with
Tailscale SaaS (previously infinite or based on token expiry).
In addition, it adds an option use the expiry time from the Token sent
by the OpenID provider. This will typically cause really short expiry
and you should only turn on this option if you know what you are
desiring.
This fixes#1176.
Co-authored-by: Even Holthe <even.holthe@bekk.no>
Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>
