proxy_cache_bypass does not work when a period characer is part of the name of a cookie

[ScottieIOT@…]

When using this directive on a location :

proxy_cache_bypass $cookie_Example.AUTH;

The resulting nginx logs show BYPASS for upstream_cache_status on all requests, even though the client browser is not sending the cookie "Example.AUTH" .

If I change the proxy_cache_bypass parameter to contain no period characters, then the caching mechanism will work as expected without the cookie, and when the cookie is sent, the upstream_cache_status shows BYPASS as expected.

I have checked all the RFC documentation on syntax of cookie name, and all the information I can find shows that a period character should be allowed in a cookie.

I tried different workarounds to this, including encapsulating the cookie variable inside of quotes , eg :
proxy_cache_bypass "$cookie_Example.AUTH";

I have also tried escaping the period, eg :
proxy_cache_bypass $cookie_Example\.AUTH;

All of the workaround attempts failed, with upstream_cache_status showing BYPASS even though the browser/curl was not sending a a cookie.

I realize that there are a lot of third party modules here, but I do not suspect that there is any conflict, and fully expect this bug to be present with only official nginx modules (proxy module specifically) being used.

[Maxim Dounin]

You can't access cookies with dots in their names using the $cookie_*, as the dot this character is not permitted in variable names and is interpreted as a part of the following static text. In your configuration examples you've configured nginx to bypass anything, as what's written is equivalent to ${cookie_Example}.AUTH and always evaluates to true.

If you want to check a cookie with various characters not allowed in variable names, consider testing the ​$http_cookie variable instead, e.g., using a ​map with regular expressions. Something like this should work:

map $http_cookie $bypass {
    ~Example\.AUTH=  1;
}

proxy_cache_bypass $bypass;