Finds the person a KDC request is about, in the trust realm the KDC would answer it in.
the Kerberos message
the trust realm a realm-prefixed /KdcProxy names, or null for the bare path, which routes by the Kerberos realm's name
/KdcProxy
a promise of { realmId, name }, or null when the request names no person this could route by
{ realmId, name }
Finds the person a KDC request is about, in the trust realm the KDC would answer it in.