Add ability to avoid "no-store" in default Cache-Control header

[mickaeltr]

Summary

By default, Spring Security only allows turning off the default Cache-Control header. I would like to be able to customize it in order to avoid the "no-store" instruction.

Actual Behavior

Default Cache-Control header is: no-cache, no-store, max-age=0, must-revalidate

That does not allow storing the HTTP response (in any browser or proxy cache). Thus, HTTP bodies must always be downloaded, even if they have not changed.

Expected Behavior

I would like to always revalidate HTTP requests and get a 304 Not Modified when relevant, instead of downloading an HTTP body that could have been stored in a browser or proxy cache.

My ideal default Cache-Control header would be: no-cache, max-age=0, must-revalidate

Version

Spring Security 5.1.3

Thanks :)

[rwinch]

If you want to do this you can disable the default cache control and then add static headers.

[mickaeltr]

Hi @rwinch,

I tried your suggestion unfortunately I cannot get the expected behavior.

First I tried to use the CacheControlHeadersWriter class, but it isn't customizable.

Then I tried a basic StaticHeadersWriter:

http
      .headers()
      .cacheControl().disable()
      .addHeaderWriter(new StaticHeadersWriter(HttpHeaders.CACHE_CONTROL, "max-age=0, no-cache, must-revalidate"));

That works fine for most resources… but those with custom Cache-Control headers are not well-treated (values are concatenated):

return ResponseEntity.ok()
      .cacheControl(CacheControl.maxAge(1, TimeUnit.HOURS))
      .body(…);

give me this: Cache-Control: max-age=3600, max-age=0, no-cache, must-revalidate

Eventually I tried to extend the StaticHeadersWriter but it does not help because the headers list is private.

Any suggestion is welcome, thanks.

[rwinch]

Thanks for the follow up @mickaeltr!

It appears the reason is that StaticHeadersWriter is adding the header without checking to see if it exists. We should add a boolean property to allow for that behavior. I created gh-6478 for it. Would you be interested in submitting a Pull Request for that? If so please claim it by commenting on the issue.

In the meantime you can do something like this:

class CustomStaticHeadersWriter implements HeaderWriter {
    private HeaderWriter delegate = new StaticHeadersWriter(HttpHeaders.CACHE_CONTROL, "max-age=0, no-cache, must-revalidate");
    public void writeHeaders(HttpServletRequest request, HttpServletResponse response) {
        if (response.containsHeader(HttpHeaders.CACHE_CONTROL)) {
            return;
        }
        delegate.writeHeaders(request, response);
    }
}

[mickaeltr]

Thanks @rwinch, I'll let you know if I manage to setup Spring Security on my machine.

[mickaeltr]

This is what my workaround looks like for the moment:

  private void allowHttpResponseStore(HttpSecurity http) throws Exception {
    // Default Cache-Control header set by Spring Security is: no-cache, no-store, max-age=0, must-revalidate
    // We removed the "no-store" so browsers and proxy caches can store the data, however they always must revalidate it
    // Thus when the response has not changed, we get a 304 Not Modified and we don't need to download it again
    http
      .headers()
      .cacheControl().disable()
      .addHeaderWriter(new DefaultCacheControlHeadersWriter("max-age=0", "no-cache", "must-revalidate"));
  }

  // Workaround for
  // - Add ability to avoid "no-store" in default Cache-Control header: https://github.com/spring-projects/spring-security/issues/6476
  // - Add StaticHeadersWriter.setIgnoreIfContainsHeader(boolean): https://github.com/spring-projects/spring-security/issues/6478
  private static class DefaultCacheControlHeadersWriter implements HeaderWriter {
    private final HeaderWriter delegate;

    private DefaultCacheControlHeadersWriter(String... cacheControlValues) {
      this.delegate = new StaticHeadersWriter(HttpHeaders.CACHE_CONTROL, cacheControlValues);
    }

    public void writeHeaders(HttpServletRequest request, HttpServletResponse response) {
      if (!response.containsHeader(HttpHeaders.CACHE_CONTROL)) {
        delegate.writeHeaders(request, response);
      }
    }
  }

[mickaeltr]

Hello,
I've been asked how this could be done now, so here is my final solution:

private void allowHttpResponseStore(HttpSecurity http) throws Exception {
  http
    .headers()
    .cacheControl()
    .disable()
    .addHeaderWriter(new StaticHeadersWriter("no-cache", "max-age=0", "must-revalidate", "private"));
}

Hope this helps