I am looking into protecting a website from CSRF attacks. Although sensitive cookies already are tagged with
same-site=lax, I would still like to implement CSRF tokens. More specifically the double submission pattern. I read that these tokens could also be generated client-side. Is this correct? I was thinking of taking the following approach:
Should these tokens be generated for each request? Or can I just generate one token and refresh that token every time the user visits again?
Would this be a good protective measure against CSRF attacks? Is the assumption correct that the attacker can not set cookies for my specific domain and can thus not generate the token themselves?
This is all about correct, yes.
If you generate a new token for each request, you will run into a race condition as setting a cookie takes some time for the browser, and one cookie can have one value at any given time. Too fast requests will send the wrong cookie value.
It is usually enough to generate one token per user session (login).
Also SameSite nowadays is increasingly accepted as the only protection against CSRF. It may or may not be enough in your usecase, depending mostly on what potential clients (which browsers) you may want to serve, ie. what will your legitimate users use, as it's their session that attackers want to exploit in case of CSRF. If you want additional protection, double submit is a reasonable solution.