tsnet,internal/client/tailscale: resolve OAuth into authkeys in tsnet (#17191)

* tsnet,internal/client/tailscale: resolve OAuth into authkeys in tsnet

Updates #8403.

* internal/client/tailscale: omit OAuth library via build tag

Updates #12614.

Signed-off-by: Naman Sood <mail@nsood.in>

cmd/tailscale/cli/up.go

@@ -12,13 +12,11 @@ import (
 	"fmt"
 	"log"
 	"net/netip"
-	"net/url"
 	"os"
 	"os/signal"
 	"reflect"
 	"runtime"
 	"sort"
-	"strconv"
 	"strings"
 	"syscall"
 	"time"
@@ -26,7 +24,7 @@ import (
 	shellquote "github.com/kballard/go-shellquote"
 	"github.com/peterbourgon/ff/v3/ffcli"
 	qrcode "github.com/skip2/go-qrcode"
-	"golang.org/x/oauth2/clientcredentials"
+	_ "tailscale.com/feature/condregister/oauthkey"
 	"tailscale.com/health/healthmsg"
 	"tailscale.com/internal/client/tailscale"
 	"tailscale.com/ipn"
@@ -566,9 +564,13 @@ func runUp(ctx context.Context, cmd string, args []string, upArgs upArgsT) (retE
 		if err != nil {
 			return err
 		}
-		authKey, err = resolveAuthKey(ctx, authKey, upArgs.advertiseTags)
-		if err != nil {
-			return err
+		// Try to use an OAuth secret to generate an auth key if that functionality
+		// is available.
+		if f, ok := tailscale.HookResolveAuthKey.GetOk(); ok {
+			authKey, err = f(ctx, authKey, strings.Split(upArgs.advertiseTags, ","))
+			if err != nil {
+				return err
+			}
 		}
 		err = localClient.Start(ctx, ipn.Options{
 			AuthKey:     authKey,
@@ -1109,90 +1111,6 @@ func exitNodeIP(p *ipn.Prefs, st *ipnstate.Status) (ip netip.Addr) {
 	return
 }
 
-// resolveAuthKey either returns v unchanged (in the common case) or, if it
-// starts with "tskey-client-" (as Tailscale OAuth secrets do) parses it like
-//
-//	tskey-client-xxxx[?ephemeral=false&bar&preauthorized=BOOL&baseURL=...]
-//
-// and does the OAuth2 dance to get and return an authkey. The "ephemeral"
-// property defaults to true if unspecified. The "preauthorized" defaults to
-// false. The "baseURL" defaults to https://api.tailscale.com.
-// The passed in tags are required, and must be non-empty. These will be
-// set on the authkey generated by the OAuth2 dance.
-func resolveAuthKey(ctx context.Context, v, tags string) (string, error) {
-	if !strings.HasPrefix(v, "tskey-client-") {
-		return v, nil
-	}
-	if tags == "" {
-		return "", errors.New("oauth authkeys require --advertise-tags")
-	}
-
-	clientSecret, named, _ := strings.Cut(v, "?")
-	attrs, err := url.ParseQuery(named)
-	if err != nil {
-		return "", err
-	}
-	for k := range attrs {
-		switch k {
-		case "ephemeral", "preauthorized", "baseURL":
-		default:
-			return "", fmt.Errorf("unknown attribute %q", k)
-		}
-	}
-	getBool := func(name string, def bool) (bool, error) {
-		v := attrs.Get(name)
-		if v == "" {
-			return def, nil
-		}
-		ret, err := strconv.ParseBool(v)
-		if err != nil {
-			return false, fmt.Errorf("invalid attribute boolean attribute %s value %q", name, v)
-		}
-		return ret, nil
-	}
-	ephemeral, err := getBool("ephemeral", true)
-	if err != nil {
-		return "", err
-	}
-	preauth, err := getBool("preauthorized", false)
-	if err != nil {
-		return "", err
-	}
-
-	baseURL := "https://api.tailscale.com"
-	if v := attrs.Get("baseURL"); v != "" {
-		baseURL = v
-	}
-
-	credentials := clientcredentials.Config{
-		ClientID:     "some-client-id", // ignored
-		ClientSecret: clientSecret,
-		TokenURL:     baseURL + "/api/v2/oauth/token",
-	}
-
-	tsClient := tailscale.NewClient("-", nil)
-	tsClient.UserAgent = "tailscale-cli"
-	tsClient.HTTPClient = credentials.Client(ctx)
-	tsClient.BaseURL = baseURL
-
-	caps := tailscale.KeyCapabilities{
-		Devices: tailscale.KeyDeviceCapabilities{
-			Create: tailscale.KeyDeviceCreateCapabilities{
-				Reusable:      false,
-				Ephemeral:     ephemeral,
-				Preauthorized: preauth,
-				Tags:          strings.Split(tags, ","),
-			},
-		},
-	}
-
-	authkey, _, err := tsClient.CreateKey(ctx, caps)
-	if err != nil {
-		return "", err
-	}
-	return authkey, nil
-}
-
 func warnOnAdvertiseRoutes(ctx context.Context, prefs *ipn.Prefs) {
 	if len(prefs.AdvertiseRoutes) > 0 || prefs.AppConnector.Advertise {
 		// TODO(jwhited): compress CheckIPForwarding and CheckUDPGROForwarding