all: implement preauth-key support with tailnet lock

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

ipn/ipnlocal/network-lock.go

@@ -6,7 +6,9 @@ package ipnlocal
 import (
 	"bytes"
 	"context"
+	"crypto/ed25519"
 	"crypto/rand"
+	"encoding/base64"
 	"encoding/binary"
 	"encoding/json"
 	"errors"
@@ -847,6 +849,40 @@ func (b *LocalBackend) NetworkLockAffectedSigs(keyID tkatype.KeyID) ([]tkatype.M
 	return resp.Signatures, nil
 }
 
+var tkaSuffixEncoder = base64.RawStdEncoding
+
+// NetworkLockWrapPreauthKey wraps a pre-auth key with information to
+// enable unattended bringup in the locked tailnet.
+//
+// The provided trusted tailnet-lock key is used to sign
+// a SigCredential structure, which is encoded along with the
+// private key and appended to the pre-auth key.
+func (b *LocalBackend) NetworkLockWrapPreauthKey(preauthKey string, tkaKey key.NLPrivate) (string, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.tka == nil {
+		return "", errNetworkLockNotActive
+	}
+
+	pub, priv, err := ed25519.GenerateKey(nil) // nil == crypto/rand
+	if err != nil {
+		return "", err
+	}
+
+	sig := tka.NodeKeySignature{
+		SigKind:        tka.SigCredential,
+		KeyID:          tkaKey.KeyID(),
+		WrappingPubkey: pub,
+	}
+	sig.Signature, err = tkaKey.SignNKS(sig.SigHash())
+	if err != nil {
+		return "", fmt.Errorf("signing failed: %w", err)
+	}
+
+	b.logf("Generated network-lock credential signature using %s", tkaKey.Public().CLIString())
+	return fmt.Sprintf("%s--TL%s-%s", preauthKey, tkaSuffixEncoder.EncodeToString(sig.Serialize()), tkaSuffixEncoder.EncodeToString(priv)), nil
+}
+
 func signNodeKey(nodeInfo tailcfg.TKASignInfo, signer key.NLPrivate) (*tka.NodeKeySignature, error) {
 	p, err := nodeInfo.NodePublic.MarshalBinary()
 	if err != nil {

ipn/localapi/localapi.go

@@ -101,6 +101,7 @@ var handler = map[string]localAPIHandler{
 	"tka/disable":                 (*Handler).serveTKADisable,
 	"tka/force-local-disable":     (*Handler).serveTKALocalDisable,
 	"tka/affected-sigs":           (*Handler).serveTKAAffectedSigs,
+	"tka/wrap-preauth-key":        (*Handler).serveTKAWrapPreauthKey,
 	"upload-client-metrics":       (*Handler).serveUploadClientMetrics,
 	"watch-ipn-bus":               (*Handler).serveWatchIPNBus,
 	"whois":                       (*Handler).serveWhoIs,
@@ -1570,6 +1571,40 @@ func (h *Handler) serveTKAModify(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(204)
 }
 
+func (h *Handler) serveTKAWrapPreauthKey(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "network-lock modify access denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != httpm.POST {
+		http.Error(w, "use POST", http.StatusMethodNotAllowed)
+		return
+	}
+
+	type wrapRequest struct {
+		TSKey  string
+		TKAKey string // key.NLPrivate.MarshalText
+	}
+	var req wrapRequest
+	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 12*1024)).Decode(&req); err != nil {
+		http.Error(w, "invalid JSON body", http.StatusBadRequest)
+		return
+	}
+	var priv key.NLPrivate
+	if err := priv.UnmarshalText([]byte(req.TKAKey)); err != nil {
+		http.Error(w, "invalid JSON body", http.StatusBadRequest)
+		return
+	}
+
+	wrappedKey, err := h.b.NetworkLockWrapPreauthKey(req.TSKey, priv)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.WriteHeader(200)
+	w.Write([]byte(wrappedKey))
+}
+
 func (h *Handler) serveTKADisable(w http.ResponseWriter, r *http.Request) {
 	if !h.PermitWrite {
 		http.Error(w, "network-lock modify access denied", http.StatusForbidden)