issuer URIs with a path part don't work

i originally opened this as https://github.com/solid/oidc-auth-manager/issues/44 but perhaps i should have started here to target the right audience.

oidc-auth-mananger seems to make an invalid assumption that all OIDC Issuers are URIs with an empty path part. if a webid has an OIDC Issuer URI with a path part (like my webid https://zenomt.zenomt.com/card.ttl#me with issuer https://zenomt.com/oidc/), it can never be matched against the id_token iss claim because the discovered issuer URI is reduced to its origin before being compared. see these lines in preferred-provider.js.

OIDC Issuers are allowed to have path parts.

src/preferred-provider.js の 70〜73 行付近から始めます。ここでは、検出された issuer URI が id_token の iss claim と比較される前に短縮されています。issuer のパス部分に関する OpenID Connect の要件を確認し、一致判定時にパスを保持してください。https://zenomt.com/oidc/ のような issuer が対応する iss claim と一致できれば完了です。