How to configure caching for static resources in Sitecore

Question

How can I enable caching for static resources such as CSS and JavaScript files in a Sitecore solution? I need these resources to have the following response header present:

Cache-Control:public, max-age=14400

I have the following settings in web.config with no success.

#1 system.webServer/caching

This breaks Sitecore completely. Returns 500 response code with no error information.

<configuration>
  <system.webServer>
    <caching enabled="true" enableKernelCache="true">
      <profiles>
        <add extension=".js" policy="CacheForTimePeriod" duration="365.00:00:00"/>
      </profiles>
    </caching>
  </system.webServer>
</configuration>

#2 system.webServer/staticContent/clientCache

This makes no change to the response headers.

<configuration>
  <system.webServer>
    <staticContent>
      <clientCache cacheControlCustom="public" cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00"/>
    </staticContent>
  </system.webServer>
</configuration>

#3 location/system.webServer/staticContent/clientCache

This also makes no change to the response headers.

<configuration>
  <location path="themes">
    <system.webServer>
      <staticContent>
        <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="00:00:15" />
      </staticContent>
    </system.webServer>
  </location>
</configuration>

Answer 1

Option #3 actually does work. I forgot to do a hard refresh in my browser during testing. Oops.

So you can add this to your main web.config

<configuration>
  <location path="themes">
    <system.webServer>
      <staticContent>
        <clientCache cacheControlCustom="public" cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00" />
      </staticContent>
    </system.webServer>
  </location>
</configuration>

Or if you prefer, you can create a new web.config in the themes folder with the following content which achieves the same thing:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.webServer>
    <staticContent>
      <clientCache cacheControlCustom="public" cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00" />
    </staticContent>
  </system.webServer>
</configuration>

When testing caching settings, don't forget to do a hard refresh!