Add method to validate configuration

cmd/command.go

@@ -1,6 +1,7 @@
 package lumecmd
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"strconv"
@@ -92,3 +93,12 @@ func GetCommand(name string) (Command, bool) {
 	cmd, ok := commandRegistry[name]
 	return cmd, ok
 }
+
+// Validate configuration struct
+func (c *Config) Validate() error {
+	var err error
+	if c.AccessToken == "" {
+		err = errors.New("access_token is not set")
+	}
+	return err
+}