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)
+}

server/domain/reconnect_test.go

@@ -1,6 +1,8 @@
 package domain
 
 import (
+	"crypto/hmac"
+	"crypto/sha256"
 	"errors"
 	"testing"
 	"time"
@@ -92,3 +94,42 @@ func TestRankedAbandonCooldownUsesRollingSevenDayLadder(t *testing.T) {
 		t.Fatalf("abandonment repeated: %+v", again)
 	}
 }
+
+func TestSignedJoinAuthorisationBindsEveryClaimBeforeReclaim(t *testing.T) {
+	now := time.Unix(1000, 0).UTC()
+	r, err := NewRankedConnections("match-1", "server-1", "v1", testRoster(now))
+	if err != nil {
+		t.Fatal(err)
+	}
+	key := []byte("test-signing-key")
+	sign := func(payload []byte) ([]byte, error) {
+		mac := hmac.New(sha256.New, key)
+		_, _ = mac.Write(payload)
+		return mac.Sum(nil), nil
+	}
+	verify := func(payload, signature []byte) bool {
+		expected, _ := sign(payload)
+		return hmac.Equal(expected, signature)
+	}
+	signed, err := SignJoinAuthorisation(testRoster(now)[0], sign)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if gen, err := r.AdmitSigned(signed, verify, now); err != nil || gen != 1 {
+		t.Fatalf("signed initial admit = %d, %v", gen, err)
+	}
+	if err := r.Disconnect("a", 1, now); err != nil {
+		t.Fatal(err)
+	}
+	tampered := signed
+	tampered.Authorisation.Slot = 1
+	if _, err := r.AdmitSigned(tampered, verify, now.Add(time.Second)); !errors.Is(err, ErrJoinAuthorisation) {
+		t.Fatalf("tampered slot accepted: %v", err)
+	}
+	if _, err := r.AdmitSigned(signed, func([]byte, []byte) bool { return false }, now.Add(RankedReconnectGrace)); !errors.Is(err, ErrJoinAuthorisation) {
+		t.Fatalf("unverified signature accepted: %v", err)
+	}
+	if gen, err := r.AdmitSigned(signed, verify, now.Add(RankedReconnectGrace)); err != nil || gen != 2 {
+		t.Fatalf("signed reclaim = %d, %v", gen, err)
+	}
+}