Vary header changed by SessionMiddleware

[y p]

To specify the cache mode, i use the view decorator like this:

@vary_on_headers('Accept', 'Accept-Language', 'Origin', 'User-Agent')
@cache_control(public=True, max_age=3600)

But after tracing, I found that SessionMiddleware modified the Vary Header and added a Cookie, as follows:

if accessed:
    patch_vary_headers(response, ('Cookie',))

Causes cache invalidation after user login again.
I have specified the cache as public, in which case the cache scheme should have nothing to do with cookies.