feat: sign reconnect authorisations

server/domain/join_auth.go

@@ -0,0 +1,37 @@
+package domain
+
+import (
+	"fmt"
+	"time"
+)
+
+// SignedJoinAuthorisation is the transport envelope. The signing primitive is
+// supplied by the backend signer so this policy stays independent of key
+// storage and cryptographic algorithm choice.
+type SignedJoinAuthorisation struct {
+	Authorisation JoinAuthorisation
+	Signature     []byte
+}
+
+func JoinAuthorisationBytes(auth JoinAuthorisation) []byte {
+	return []byte(fmt.Sprintf("%s\x00%s\x00%s\x00%s\x00%d\x00%d\x00%s\x00%d\x00%s",
+		auth.MatchID, auth.ServerID, auth.PlayerID, auth.SteamID, auth.Slot, auth.Team, auth.Protocol, auth.Generation, auth.ExpiresAt.UTC().Format(time.RFC3339Nano)))
+}
+
+func SignJoinAuthorisation(auth JoinAuthorisation, sign func([]byte) ([]byte, error)) (SignedJoinAuthorisation, error) {
+	if sign == nil {
+		return SignedJoinAuthorisation{}, ErrJoinAuthorisation
+	}
+	signature, err := sign(JoinAuthorisationBytes(auth))
+	if err != nil || len(signature) == 0 {
+		return SignedJoinAuthorisation{}, ErrJoinAuthorisation
+	}
+	return SignedJoinAuthorisation{Authorisation: auth, Signature: append([]byte(nil), signature...)}, nil
+}
+
+func (r *RankedConnections) AdmitSigned(signed SignedJoinAuthorisation, verify func([]byte, []byte) bool, now time.Time) (uint64, error) {
+	if len(signed.Signature) == 0 || verify == nil || !verify(JoinAuthorisationBytes(signed.Authorisation), signed.Signature) {
+		return 0, ErrJoinAuthorisation
+	}
+	return r.Admit(signed.Authorisation, now)
+}