TS2021: Convert /key handler to send the Noise key too

api.go

@@ -9,6 +9,7 @@ import (
 	"html/template"
 	"io"
 	"net/http"
+	"strconv"
 	"strings"
 	"time"
 
@@ -28,11 +29,40 @@ const (
 	ErrRegisterMethodCLIDoesNotSupportExpire = Error(
 		"machines registered with CLI does not support expire",
 	)
+
+	// The CapabilityVersion is used by Tailscale clients to indicate
+	// their codebase version. Tailscale clients can communicate over TS2021
+	// from CapabilityVersion 28.
+	// See https://github.com/tailscale/tailscale/blob/main/tailcfg/tailcfg.go
+	NoiseCapabilityVersion = 28
 )
 
 // KeyHandler provides the Headscale pub key
 // Listens in /key.
 func (h *Headscale) KeyHandler(ctx *gin.Context) {
+	// New Tailscale clients send a 'v' parameter to indicate the CurrentCapabilityVersion
+	clientCapabilityStr := ctx.Query("v")
+	if clientCapabilityStr != "" {
+		clientCapabilityVersion, err := strconv.Atoi(clientCapabilityStr)
+		if err != nil {
+			ctx.String(http.StatusBadRequest, "Invalid version")
+
+			return
+		}
+
+		if clientCapabilityVersion >= NoiseCapabilityVersion {
+			// Tailscale has a different key for the TS2021 protocol
+			resp := tailcfg.OverTLSPublicKeyResponse{
+				LegacyPublicKey: h.privateKey.Public(),
+				PublicKey:       h.noisePrivateKey.Public(),
+			}
+			ctx.JSON(http.StatusOK, resp)
+
+			return
+		}
+	}
+
+	// Old clients don't send a 'v' parameter, so we send the legacy public key
 	ctx.Data(
 		http.StatusOK,
 		"text/plain; charset=utf-8",