Use constant time comparisons for CSRF tokens

[rwinch]

While it is not a practical exploit at this point, it is best to be defensive. We should change CSRF token comparison to use a constant time comparison to avoid side channel attacks.

NOTE: This was originally reported via Xhelal Likaj, xhelallikaj20@gmail.com

[ogarber]

Hi @rwinch , I have a question: will this fix also be merged in the older pipe-lines (I'm interesting in 5.2.x...).
Thank you in advance

[ogarber]

Hi @rwinch , sorry for annoying...
Did you see my previous comment?

[japavinayteja]

Hi @rwinch, will this fix will be merged in older versions like 5.2.x or when can we expect this release