Web Agent does not yet support setting the SameSite cookie.
However, there are ways to workaround it until it is officially supported.
Any web servers would have the feature to rewrite the cookies going out to the browser.
In case of Apache, you can do the following.
Modify the httpd.conf file as below.
1. Load the mod_headers.so
LoadModule headers_module modules/mod_headers.so
2. Rewrite the cookie
Header edit Set-Cookie ^(.*)$ "$1; SameSite=Strict"
Once you set the above 2 lines and restart the Apache, all cookies would be adding the SameSite flag.