Detect Set-Cookie expiration - haproxy

Question

I want to be able to detect when a response from the backend contains this:
testCookie="ASF#ED124312FASdf23er="; Version=1; Max-Age=0; Expires=Thu, 01 Jan 1970 00:00:10 GMT; Path=/; Secure
What I want to detect is that the response is going to set the expiration date to 01 Jan 1970 for the cookie called testCookie.
The challenge is in the fact that haproxy when using a fetch method to get a header, will consider commas as the delimiter for separate values. and the alternative proposed, which is to use fhdr to fetch the complete header indeed works but will not enable you to filter for a specific Set-Cookie header via a regex filter or something, so you have to rely on a fixed index of the Set-Cookie header to be fetched....and that is not acceptable obviously.
So, I have tried:
ACL with regex
acl is_expiration hdr_reg(Set-Cookie) <enter_regex_here>
This has the downside that the comma in the expiration date will cause haproxy to parse that value in 2 separate parts so you can either match the first part which gives you the correct cookie identifier or the second part which has the expiration date.
Full Header with var and separate acl
http-response set-var(txn.temp_var) res.fhdr(Set-Cookie)
acl is_expiration var(txn.temp_var) -m sub 01\ Jan\ 1970
This will store the whole text in the Set-Cookie header in a temporary value and then I can do a substring match on that, or a regular expression but I still run into the problem of the comma and this is approach is error prone because it will take the first Set-Cookie header found or one found at a specific index I can specify.
Workaround
I could match by the Max-Age but if the server implementation changes and Expires and Max-Age switch places, I am screwed.
acl is_expiration hdr_reg(Set-Cookie) testCookie.*Max-Age=0
So.....heeeeelp!!!

Answer 1

After getting my head a bit out of the issue itself, I found an answer showing how the synthax should look like for an ACL using the full header fetch command.
Bottom line....the documentation is kind of quirky and the solution looks like this:
acl is_expiration res.fhdr(Set-Cookie) -m reg testCookie.*Expires=Thu,\ 01\ Jan\ 1970