fix: use mb_strtolower to convert login name

Signed-off-by: Cleopatra Enjeck M. <patrathewhiz@gmail.com>

Author: enjeck

lib/private/User/Session.php

@@ -780,7 +780,7 @@ private function validateToken($token, $user = null) {
 	 * Check if login names match
 	 */
 	private function validateTokenLoginName(?string $loginName, IToken $token): bool {
-		if (strcasecmp($token->getLoginName(), $loginName ?? '') !== 0) {
+		if (mb_strtolower($token->getLoginName()) !== mb_strtolower($loginName ?? '')) {
 			// TODO: this makes it impossible to use different login names on browser and client
 			// e.g. login by e-mail 'user@example.com' on browser for generating the token will not
 			//      allow to use the client token with the login name 'user'.