cmd/tailscale/cli: support passing network lock keys via files

Fixes tailscale/corp#22356

Change-Id: I959efae716a22bcf582c20d261fb1b57bacf6dd9
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/k8s-operator/depaware.txt

@@ -747,7 +747,7 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         tailscale.com/taildrop                                       from tailscale.com/ipn/ipnlocal+
         tailscale.com/tempfork/heap                                  from tailscale.com/wgengine/magicsock
         tailscale.com/tka                                            from tailscale.com/client/tailscale+
-   W    tailscale.com/tsconst                                        from tailscale.com/net/netmon+
+        tailscale.com/tsconst                                        from tailscale.com/net/netmon+
         tailscale.com/tsd                                            from tailscale.com/ipn/ipnlocal+
         tailscale.com/tsnet                                          from tailscale.com/cmd/k8s-operator+
         tailscale.com/tstime                                         from tailscale.com/cmd/k8s-operator+

cmd/tailscale/cli/network-lock.go

@@ -20,6 +20,7 @@
 	"github.com/peterbourgon/ff/v3/ffcli"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/tka"
+	"tailscale.com/tsconst"
 	"tailscale.com/types/key"
 	"tailscale.com/types/tkatype"
 )
@@ -443,15 +444,33 @@ func runNetworkLockModify(ctx context.Context, addArgs, removeArgs []string) err
 
 var nlSignCmd = &ffcli.Command{
 	Name:       "sign",
-	ShortUsage: "tailscale lock sign <node-key> [<rotation-key>] or sign <auth-key>",
+	ShortUsage: "tailscale lock sign <node-key> [<rotation-key>]\ntailscale lock sign <auth-key>",
 	ShortHelp:  "Signs a node or pre-approved auth key",
 	LongHelp: `Either:
-  - signs a node key and transmits the signature to the coordination server, or
+  - signs a node key and transmits the signature to the coordination
-  - signs a pre-approved auth key, printing it in a form that can be used to bring up nodes under tailnet lock`,
+    server, or
+  - signs a pre-approved auth key, printing it in a form that can be
+    used to bring up nodes under tailnet lock
+
+If any of the key arguments begin with "file:", the key is retrieved from
+the file at the path specified in the argument suffix.`,
 	Exec: runNetworkLockSign,
 }
 
 func runNetworkLockSign(ctx context.Context, args []string) error {
+	// If any of the arguments start with "file:", replace that argument
+	// with the contents of the file. We do this early, before the check
+	// to see if the first argument is an auth key.
+	for i, arg := range args {
+		if filename, ok := strings.CutPrefix(arg, "file:"); ok {
+			b, err := os.ReadFile(filename)
+			if err != nil {
+				return err
+			}
+			args[i] = strings.TrimSpace(string(b))
+		}
+	}
+
 	if len(args) > 0 && strings.HasPrefix(args[0], "tskey-auth-") {
 		return runTskeyWrapCmd(ctx, args)
 	}
@@ -476,7 +495,7 @@ func runNetworkLockSign(ctx context.Context, args []string) error {
 	err := localClient.NetworkLockSign(ctx, nodeKey, []byte(rotationKey.Verifier()))
 	// Provide a better help message for when someone clicks through the signing flow
 	// on the wrong device.
-	if err != nil && strings.Contains(err.Error(), "this node is not trusted by network lock") {
+	if err != nil && strings.Contains(err.Error(), tsconst.TailnetLockNotTrustedMsg) {
 		fmt.Fprintln(Stderr, "Error: Signing is not available on this device because it does not have a trusted tailnet lock key.")
 		fmt.Fprintln(Stderr)
 		fmt.Fprintln(Stderr, "Try again on a signing device instead. Tailnet admins can see signing devices on the admin panel.")

cmd/tailscale/depaware.txt

@@ -128,7 +128,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/tailcfg                                        from tailscale.com/client/tailscale+
         tailscale.com/tempfork/spf13/cobra                           from tailscale.com/cmd/tailscale/cli/ffcomplete+
         tailscale.com/tka                                            from tailscale.com/client/tailscale+
-   W    tailscale.com/tsconst                                        from tailscale.com/net/netmon+
+        tailscale.com/tsconst                                        from tailscale.com/net/netmon+
         tailscale.com/tstime                                         from tailscale.com/control/controlhttp+
         tailscale.com/tstime/mono                                    from tailscale.com/tstime/rate
         tailscale.com/tstime/rate                                    from tailscale.com/cmd/tailscale/cli+

cmd/tailscaled/depaware.txt

@@ -338,7 +338,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
   LD    tailscale.com/tempfork/gliderlabs/ssh                        from tailscale.com/ssh/tailssh
         tailscale.com/tempfork/heap                                  from tailscale.com/wgengine/magicsock
         tailscale.com/tka                                            from tailscale.com/client/tailscale+
-   W    tailscale.com/tsconst                                        from tailscale.com/net/netmon+
+        tailscale.com/tsconst                                        from tailscale.com/net/netmon+
         tailscale.com/tsd                                            from tailscale.com/cmd/tailscaled+
         tailscale.com/tstime                                         from tailscale.com/control/controlclient+
         tailscale.com/tstime/mono                                    from tailscale.com/net/tstun+

ipn/ipnlocal/network-lock.go

@@ -27,6 +27,7 @@
 	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tka"
+	"tailscale.com/tsconst"
 	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/netmap"
@@ -716,7 +717,7 @@ func (b *LocalBackend) NetworkLockSign(nodeKey key.NodePublic, rotationPublic []
 			return key.NodePublic{}, tka.NodeKeySignature{}, errNetworkLockNotActive
 		}
 		if !b.tka.authority.KeyTrusted(nlPriv.KeyID()) {
-			return key.NodePublic{}, tka.NodeKeySignature{}, errors.New("this node is not trusted by network lock")
+			return key.NodePublic{}, tka.NodeKeySignature{}, errors.New(tsconst.TailnetLockNotTrustedMsg)
 		}
 
 		p, err := nodeKey.MarshalBinary()

tsconst/interface.go

@@ -9,3 +9,7 @@
 // interfaces on Windows. This is set by the WinTun driver.
 const WintunInterfaceDesc = "Tailscale Tunnel"
 const WintunInterfaceDesc0_14 = "Wintun Userspace Tunnel"
+
+// TailnetLockNotTrustedMsg is the error message used by network lock
+// and sniffed (via substring) out of an error sent over the network.
+const TailnetLockNotTrustedMsg = "this node is not trusted by network lock"