add acl helper functionalities (#3831)

weed/s3api/s3_constants/acp_grantee_group.go

@@ -6,3 +6,15 @@ var (
 	GranteeGroupAuthenticatedUsers = "http://acs.amazonaws.com/groups/global/AuthenticatedUsers"
 	GranteeGroupLogDelivery        = "http://acs.amazonaws.com/groups/s3/LogDelivery"
 )
+
+func ValidateGroup(group string) bool {
+	valid := true
+	switch group {
+	case GranteeGroupAllUsers:
+	case GranteeGroupLogDelivery:
+	case GranteeGroupAuthenticatedUsers:
+	default:
+		valid = false
+	}
+	return valid
+}