diff --git a/main.go b/main.go
index b05f1467..0fb0d0f5 100644
--- a/main.go
+++ b/main.go
@@ -70,6 +70,7 @@ func main() {
 	flagSet.String("google-service-account-json", "", "the path to the service account json credentials")
 	flagSet.String("client-id", "", "the OAuth Client ID: ie: \"123456.apps.googleusercontent.com\"")
 	flagSet.String("client-secret", "", "the OAuth Client Secret")
+	flagSet.String("client-secret-file", "", "the file with OAuth Client Secret")
 	flagSet.String("authenticated-emails-file", "", "authenticate against emails via file (one per line)")
 	flagSet.String("htpasswd-file", "", "additionally authenticate against a htpasswd file. Entries must be created with \"htpasswd -s\" for SHA encryption or \"htpasswd -B\" for bcrypt encryption")
 	flagSet.Bool("display-htpasswd-form", true, "display username / password login form if an htpasswd file is provided")