fix: ensure we don't reject tokens with unknown fields

Author: davidzhao

auth/grants.go

@@ -35,6 +35,12 @@ var tokenMarshaler = protojson.MarshalOptions{
 	EmitDefaultValues: false,
 }
 
+// tokenUnmarshaler discards unknown fields so that older servers can accept
+// tokens issued by newer clients that include fields the server does not yet know about.
+var tokenUnmarshaler = protojson.UnmarshalOptions{
+	DiscardUnknown: true,
+}
+
 var ErrSensitiveCredentials = errors.New("room configuration should not contain sensitive credentials")
 
 func (c *RoomConfiguration) Clone() *RoomConfiguration {
@@ -49,7 +55,7 @@ func (c *RoomConfiguration) MarshalJSON() ([]byte, error) {
 }
 
 func (c *RoomConfiguration) UnmarshalJSON(data []byte) error {
-	return protojson.Unmarshal(data, (*livekit.RoomConfiguration)(c))
+	return tokenUnmarshaler.Unmarshal(data, (*livekit.RoomConfiguration)(c))
 }
 
 // CheckCredentials checks if the room configuration contains sensitive credentials

auth/verifier_test.go

@@ -18,7 +18,9 @@ import (
 	"testing"
 	"time"
 
+	"github.com/go-jose/go-jose/v3"
 	"github.com/go-jose/go-jose/v3/json"
+	"github.com/go-jose/go-jose/v3/jwt"
 	"github.com/stretchr/testify/require"
 
 	"github.com/livekit/protocol/auth"
@@ -95,6 +97,42 @@ func TestVerifier(t *testing.T) {
 		require.EqualValues(t, attrs, decoded.Attributes)
 	})
 
+	t.Run("unknown roomConfig fields are ignored for forward compatibility", func(t *testing.T) {
+		// Simulate a token issued by a newer client whose RoomConfiguration includes
+		// a field this server's proto does not yet know about. The server should
+		// still accept the token rather than failing with `unknown field`.
+		sig, err := jose.NewSigner(
+			jose.SigningKey{Algorithm: jose.HS256, Key: []byte(secret)},
+			(&jose.SignerOptions{}).WithType("JWT"),
+		)
+		require.NoError(t, err)
+
+		claims := map[string]interface{}{
+			"iss": apiKey,
+			"sub": "me",
+			"nbf": jwt.NewNumericDate(time.Now()),
+			"exp": jwt.NewNumericDate(time.Now().Add(time.Minute)),
+			"video": map[string]interface{}{
+				"roomJoin": true,
+				"room":     "myroom",
+			},
+			"roomConfig": map[string]interface{}{
+				"name":                "myroom",
+				"someFutureFieldName": "future-value",
+			},
+		}
+		token, err := jwt.Signed(sig).Claims(claims).CompactSerialize()
+		require.NoError(t, err)
+
+		v, err := auth.ParseAPIToken(token)
+		require.NoError(t, err)
+
+		_, decoded, err := v.Verify(secret)
+		require.NoError(t, err)
+		require.NotNil(t, decoded.RoomConfig)
+		require.Equal(t, "myroom", decoded.RoomConfig.Name)
+	})
+
 	t.Run("nil permissions are handled", func(t *testing.T) {
 		grant := &auth.VideoGrant{
 			Room:     "myroom",