cmd/tailscale: add id-token subcommand

RELNOTE=Initial support for getting OIDC ID Tokens

Updates tailscale/corp#4347

Signed-off-by: Maisem Ali <maisem@tailscale.com>

client/tailscale/tailscale.go

@@ -275,6 +275,21 @@ func status(ctx context.Context, queryString string) (*ipnstate.Status, error) {
 	return st, nil
 }
 
+// IDToken is a request to get an OIDC ID token for an audience.
+// The token can be presented to any resource provider which offers OIDC
+// Federation.
+func IDToken(ctx context.Context, aud string) (*tailcfg.TokenResponse, error) {
+	body, err := get200(ctx, "/localapi/v0/id-token?aud="+url.QueryEscape(aud))
+	if err != nil {
+		return nil, err
+	}
+	tr := new(tailcfg.TokenResponse)
+	if err := json.Unmarshal(body, tr); err != nil {
+		return nil, err
+	}
+	return tr, nil
+}
+
 func WaitingFiles(ctx context.Context) ([]apitype.WaitingFile, error) {
 	body, err := get200(ctx, "/localapi/v0/files/")
 	if err != nil {

cmd/tailscale/cli/cli.go

@@ -25,6 +25,7 @@
 
 	"github.com/peterbourgon/ff/v3/ffcli"
 	"tailscale.com/client/tailscale"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/paths"
 	"tailscale.com/safesocket"
@@ -173,6 +174,9 @@ func Run(args []string) (err error) {
 	for _, c := range rootCmd.Subcommands {
 		c.UsageFunc = usageFunc
 	}
+	if envknob.UseWIPCode() {
+		rootCmd.Subcommands = append(rootCmd.Subcommands, idTokenCmd)
+	}
 
 	// Don't advertise the debug command, but it exists.
 	if strSliceContains(args, "debug") {

cmd/tailscale/cli/id-token.go

@@ -0,0 +1,35 @@
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/peterbourgon/ff/v3/ffcli"
+	"tailscale.com/client/tailscale"
+)
+
+var idTokenCmd = &ffcli.Command{
+	Name:       "id-token",
+	ShortUsage: "id-token <aud>",
+	ShortHelp:  "fetch an OIDC id-token for the Tailscale machine",
+	Exec:       runIDToken,
+}
+
+func runIDToken(ctx context.Context, args []string) error {
+	if len(args) != 1 {
+		return errors.New("usage: id-token <aud>")
+	}
+
+	tr, err := tailscale.IDToken(ctx, args[0])
+	if err != nil {
+		return err
+	}
+
+	fmt.Println(tr.IDToken)
+	return nil
+}

ipn/localapi/localapi.go

@@ -25,7 +25,6 @@
 
 	"inet.af/netaddr"
 	"tailscale.com/client/tailscale/apitype"
-	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/ipn/ipnstate"
@@ -145,10 +144,6 @@ func (h *Handler) serveIDToken(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "id-token access denied", http.StatusForbidden)
 		return
 	}
-	if !envknob.UseWIPCode() {
-		http.Error(w, "id-token access denied", http.StatusServiceUnavailable)
-		return
-	}
 	nm := h.b.NetMap()
 	if nm == nil {
 		http.Error(w, "no netmap", http.StatusServiceUnavailable)