To set the HttpOnly flag for the cookies being used in .htaccess, you can add the following code to your .htaccess file:
<IfModule mod_headers.c>
Header edit Set-Cookie ^(.*)$ $1;HttpOnly
</IfModule>
This will ensure that all cookies set by your website have the HttpOnly flag set, which means that they can only be accessed by the server and not by client-side scripts. This helps to prevent certain types of attacks, such as cross-site scripting (XSS), which can compromise the security of your website.
Note: This solution assumes that your website is using Apache as its web server. If you are using a different web server, the exact syntax of the code may vary. You should consult the documentation for your specific web server for more information.