Support RCF 9207 - issuer check

[uvdsl]

Following the discussion in https://github.com/solid/solid-oidc/issues/221, CSS/Pivot, ESS and TrinPod all support the issuer check recommended by RFC 9207.

As discussed in https://github.com/uvdsl/solid-oidc-client-browser/issues/12, a client could accept sessions where the RFC 9207 implemented - but given the discussion in https://github.com/solid/solid-oidc/issues/221, I think that RFC 9207 MUST be implemented by identity providers.

Therefore, I think it would be great if NSS implemented RFC 9207.