Pomerium Pre-Auth Memory Exhaustion via Unbounded zstd Decompression in HPKE Callback

Summary The HPKE V2 URL decode path in pkg/hpke/url.go decompresses attacker-controlled zstd data without any size limit. On Pomerium deployments using the stateless authentication flow Pomerium Zero / hosted authenticate, the proxy's /.pomerium/callback endpoint is reachable without credentials...