diff --git a/ldap/client.go b/ldap/client.go
index b57ebb8..e559c46 100644
--- a/ldap/client.go
+++ b/ldap/client.go
@@ -273,7 +273,7 @@ func (c *Client) Authenticate(ctx context.Context, username, password string, op
 			return nil, fmt.Errorf("%s: failed to get user attributes: %w", op, err)
 		}
 		for _, a := range attrs {
-			userAttrs[a.Name] = a.Vals
+			userAttrs[strings.ToLower(a.Name)] = a.Vals
 		}
 	}
 	if !opts.withGroups && !c.conf.IncludeUserGroups {