minecraft/dial.go: Read DisplayName from Mojang chain after authentic…

…ation and set it correctly in the client data.

This fixes a method to detect gophertunnel clients.

minecraft/dial.go

@@ -7,6 +7,7 @@ import (
 	"crypto/elliptic"
 	"crypto/rand"
 	"encoding/base64"
+	"encoding/json"
 	"fmt"
 	"github.com/google/uuid"
 	"github.com/sandertv/go-raknet"
@@ -16,6 +17,7 @@ import (
 	"github.com/sandertv/gophertunnel/minecraft/protocol/login"
 	"github.com/sandertv/gophertunnel/minecraft/protocol/packet"
 	"golang.org/x/oauth2"
+	"gopkg.in/square/go-jose.v2/jwt"
 	"log"
 	rand2 "math/rand"
 	"net"
@@ -153,6 +155,7 @@ func (d Dialer) DialContext(ctx context.Context, network, address string) (conn
 		if err != nil {
 			return nil, &net.OpError{Op: "dial", Net: "minecraft", Err: err}
 		}
+		d.IdentityData = readChainIdentityData([]byte(chainData))
 	}
 	if d.ErrorLog == nil {
 		d.ErrorLog = log.New(os.Stderr, "", log.LstdFlags)
@@ -248,6 +251,30 @@ func (d Dialer) DialContext(ctx context.Context, network, address string) (conn
 	}
 }
 
+// readChainIdentityData reads a login.IdentityData from the Mojang chain
+// obtained through authentication.
+func readChainIdentityData(chainData []byte) login.IdentityData {
+	chain := struct{ Chain []string }{}
+	if err := json.Unmarshal(chainData, &chain); err != nil {
+		panic("invalid chain data from authentication: " + err.Error())
+	}
+	data := chain.Chain[1]
+	claims := struct {
+		ExtraData login.IdentityData `json:"extraData"`
+	}{}
+	tok, err := jwt.ParseSigned(data)
+	if err != nil {
+		panic("invalid chain data from authentication: " + err.Error())
+	}
+	if err := tok.UnsafeClaimsWithoutVerification(&claims); err != nil {
+		panic("invalid chain data from authentication: " + err.Error())
+	}
+	if claims.ExtraData.Identity == "" {
+		panic("chain data contained no data")
+	}
+	return claims.ExtraData
+}
+
 // listenConn listens on the connection until it is closed on another goroutine. The channel passed will
 // receive a value once the connection is logged in.
 func listenConn(conn *Conn, logger *log.Logger, l, c chan struct{}) {