Fix linter errors.

cmd/headscale/cli/debug.go

@@ -9,6 +9,16 @@ import (
 	"google.golang.org/grpc/status"
 )
 
+const (
+	keyLength             = 64
+	errPreAuthKeyTooShort = Error("key too short, must be 64 hexadecimal characters")
+)
+
+// Error is used to compare errors as per https://dave.cheney.net/2016/04/07/constant-errors
+type Error string
+
+func (e Error) Error() string { return string(e) }
+
 func init() {
 	rootCmd.AddCommand(debugCmd)
 
@@ -77,8 +87,8 @@ var createNodeCmd = &cobra.Command{
 
 			return
 		}
-		if len(machineKey) != 64 {
+		if len(machineKey) != keyLength {
-			err = fmt.Errorf("key '%s' too short, must be 64 hexadecimal characters", machineKey)
+			err = errPreAuthKeyTooShort
 			ErrorOutput(
 				err,
 				fmt.Sprintf("Error: %s", err),