How to have nginx proxy_pass follow upstream 302 redirects (eg, when you're running a steam cache and you're behind Cox's layer 7 interception stuff)

proxy.conf

# This config came around after a friend had problems with a Steam cache on his
# Cox internet connection. Cox would intercept any requests to Steam content
# servers and return a 302 to Cox's servers. The cache would return the 302
# to the Steam client, and the Steam client would go directly to Cox, bypassing
# the cache.
# This config makes nginx follow the 302 itself, and caches the result of the
# redirect as if it was the response to the original request. So subsequent
# requests to the URL that returned a 302 will get the file instead of a 302.


proxy_cache_path /cache keys_zone=steam:100m levels=1:2 inactive=100d max_size=1000g;

server {
    listen      80;
    charset     utf-8;

    client_max_body_size 75M;

    # main cache block - when upstream responds with a 302, it's caught by 
    # error_page and passed off to the (nearly identical) @handle_redirects
    location / {
       proxy_pass http://web;
       proxy_cache       steam;
       proxy_cache_key   $uri;
       proxy_cache_valid 200 206 3000h;
       proxy_intercept_errors on;
       error_page 301 302 307 = @handle_redirects;
    }

    location @handle_redirects {
       #store the current state of the world so we can reuse it in a minute
       # We need to capture these values now, because as soon as we invoke 
       # the proxy_* directives, these will disappear
       set $original_uri $uri;
       set $orig_loc $upstream_http_location;

       # nginx goes to fetch the value from the upstream Location header
       proxy_pass $orig_loc;
       proxy_cache       steam;
       # But we store the result with the cache key of the original request URI
       # so that future clients don't need to follow the redirect too
       proxy_cache_key $original_uri;
       proxy_cache_valid 200 206 3000h;
    }
}