all: implement preauth-key support with tailnet lock

Signed-off-by: Tom DNetto <tom@tailscale.com>

client/tailscale/localclient.go

@@ -850,6 +850,30 @@ func (lc *LocalClient) NetworkLockInit(ctx context.Context, keys []tka.Key, disa
 	return decodeJSON[*ipnstate.NetworkLockStatus](body)
 }
 
+// NetworkLockWrapPreauthKey wraps a pre-auth key with information to
+// enable unattended bringup in the locked tailnet.
+func (lc *LocalClient) NetworkLockWrapPreauthKey(ctx context.Context, preauthKey string, tkaKey key.NLPrivate) (string, error) {
+	encodedPrivate, err := tkaKey.MarshalText()
+	if err != nil {
+		return "", err
+	}
+
+	var b bytes.Buffer
+	type wrapRequest struct {
+		TSKey  string
+		TKAKey string // key.NLPrivate.MarshalText
+	}
+	if err := json.NewEncoder(&b).Encode(wrapRequest{TSKey: preauthKey, TKAKey: string(encodedPrivate)}); err != nil {
+		return "", err
+	}
+
+	body, err := lc.send(ctx, "POST", "/localapi/v0/tka/wrap-preauth-key", 200, &b)
+	if err != nil {
+		return "", fmt.Errorf("error: %w", err)
+	}
+	return string(body), nil
+}
+
 // NetworkLockModify adds and/or removes key(s) to the tailnet key authority.
 func (lc *LocalClient) NetworkLockModify(ctx context.Context, addKeys, removeKeys []tka.Key) error {
 	var b bytes.Buffer