autopilotserver/mock: upgrade mock for session linking

autopilotserver/mock/server.go

@@ -8,6 +8,8 @@ import (
 	"sync"
 
 	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/ecdsa"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/lightninglabs/lightning-terminal/autopilotserverrpc"
 	"github.com/lightninglabs/lightning-terminal/rules"
 	"github.com/lightningnetwork/lnd/lntest/node"
@@ -44,6 +46,7 @@ type ClientState uint8
 const (
 	ClientStateActive = iota
 	ClientStateInactive
+	ClientStateRevoked
 )
 
 type clientSession struct {
@@ -172,6 +175,32 @@ func (m *Server) RegisterSession(_ context.Context,
 		return nil, err
 	}
 
+	// If linked session, check that signature is valid.
+	if len(req.GroupResponderKey) != 0 {
+		// Check that the group key is a known key.
+		_, ok := m.sessions[hex.EncodeToString(req.GroupResponderKey)]
+		if !ok {
+			return nil, fmt.Errorf("unknown group key")
+		}
+
+		// Check that the signature provided is valid.
+		sig, err := ecdsa.ParseDERSignature(req.GroupResponderSig)
+		if err != nil {
+			return nil, err
+		}
+
+		msg := chainhash.HashB(req.ResponderPubKey)
+
+		groupKey, err := btcec.ParsePubKey(req.GroupResponderKey)
+		if err != nil {
+			return nil, err
+		}
+
+		if !sig.Verify(msg, groupKey) {
+			return nil, fmt.Errorf("invalid signature")
+		}
+	}
+
 	m.sessions[hex.EncodeToString(req.ResponderPubKey)] = &clientSession{
 		key:   priv,
 		state: ClientStateActive,
@@ -209,7 +238,12 @@ func (m *Server) RevokeSession(_ context.Context,
 	m.sessMu.Lock()
 	defer m.sessMu.Unlock()
 
-	delete(m.sessions, hex.EncodeToString(req.ResponderPubKey))
+	sess, ok := m.sessions[hex.EncodeToString(req.ResponderPubKey)]
+	if !ok {
+		return nil, nil
+	}
+
+	sess.state = ClientStateRevoked
 
 	return &autopilotserverrpc.RevokeSessionResponse{}, nil
 }