GHSA-p279-2cqp-84jg: OpenDJ SASL PLAIN authzid bypassing the proxy ACI scope check

When a SASL PLAIN bind supplies an authorization identity (authzid) that resolves to a different user, PlainSASLMechanismHandler verified only the PROXIED_AUTH privilege and never evaluated the “proxy” access-control right (the mayProxy ACI scope check). As a result, any account holding the proxied-auth privilege could assume any resolvable non-root identity without being granted a proxy ACI for that target.

This diverges from every other proxy path in OpenDJ — the proxied-authorization controls (RFC 4370) and the DIGEST-MD5 / GSSAPI authzid handlers all require both the privilege and the mayProxy scope grant.