Ignoring cookies list efficiently in NGINX reverse proxy setup

What exactly are you trying to do?

The way you're doing it, by trying to blacklist only certain cookies from being cached, through if ($http_cookie …, is a wrong approach — this means that one day, someone will find a cookie that is not blacklisted, and which your backend would nonetheless accept, and cause you cache poisoning or other security issues down the line.

There's also no reason to use the http://nginx.org/r/map approach to get the values of the individual cookies, either — all of this is already available through the http://nginx.org/r/$cookie_ paradigm, making the map code for parsing out $http_cookie rather redundant and unnecessary.

Are there any cookies which you actually want to cache? If not, why not just use proxy_no_cache $http_cookie; to disallow caching when any cookies are present?

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What you'd probably want to do is first have a spec of what must be cached and under what circumstances, only then resorting to expressing such logic in a programming language like nginx.conf.

For example, a better approach would be to see which URLs should always be cached, clearing out the Cookie header to ensure that cache poisoning isn't possible (proxy_set_header Cookie "";). Else, if any cookies are present, it may either make sense to not cache anything at all (proxy_no_cache $http_cookie;), or to structure the cache such that certain combination of authentication credentials are used for http://nginx.org/r/proxy_cache_key; in this case, it might also make sense to reconstruct the Cookie request header manually through a whitelist-based approach to avoid cache-poisoning issues.