Do a refactoring to the CSRF related code, remove most unnecessary functions.
Parse the generated token's issue time, regenerate the token every a few minutes.
Add SameSite setting for cookies and rationalise the cookie setting code. Switches SameSite to Lax by default.
There is a possible future extension of differentiating which cookies could be set at Strict by default but that is for a future PR.
Fix #5583
Signed-off-by: Andrew Thornton <art27@cantab.net>
