Defence-in-depth fixes to the OIDC login flow.
Set the state/nonce cookie Secure flag from the configured server_url
scheme rather than req.TLS, so the cookies stay Secure behind a
TLS-terminating reverse proxy where the proxy-to-Headscale hop is plain
HTTP. Deriving it from config avoids trusting a spoofable
X-Forwarded-Proto header.
Make the OIDC state single-use: consume it from the cache on the
callback and clear the state/nonce cookies once validated, so a replayed
callback cannot resolve the same session and the cookies do not linger
until expiry.
Bound OIDC discovery to the caller's context so a slow or unreachable
issuer fails startup within the timeout instead of hanging, and validate
the issuer URL and required client_id/client_secret at config load so an
unworkable setup fails fast.
622e08f5e6