Understanding proxy_cache_bypass $http_cache_control

According to Nginx's doc on proxy_cache_bypass

Defines conditions under which the response will not be taken from a cache. If at least one value of the string parameters is not empty and is not equal to “0” then the response will not be taken from the cache:

I want the request with the header Cache-Control: no-cache to bypass the Nginx cache and be forwarded to the upstream service. Shall I use the following config?

proxy_cache_bypass $http_cache_control;

I asked because it seems Nginx will bypass the cache whenever the Cache-Control has non-zero value without checking if its content is no-cache. If not, what would be the best way to achieve my goal?

You are correct. You should use a map to select the correct value to control the cache.

For example:

map $http_cache_control $cache_bypass {
    no-cache   1;
}

proxy_cache_bypass $cache_bypass;

Note that the map block must be placed outside of the server block.