Onebox previews are not working for my site

Product Support
3

i see, i have reconfigured the site to treat HEAD requests identically to GET requests.

the site has a security policy that will return 400 unless the client sends a user agent string that starts with the string "Discourse Forum Onebox" and an Accept-Language: * header. i am able to pass the filter using curl with the following settings:

$ curl -v -I --http1.1 \
    -A 'Discourse Forum Onebox v3.3.0.beta1-dev' \
    -H 'Accept-Language: *' \
    https://swiftinit.org -o /dev/null

> HEAD / HTTP/1.1
> Host: swiftinit.org
> User-Agent: Discourse Forum Onebox v3.3.0.beta1-dev
> Accept: */*
> Accept-Language: *
> 

< HTTP/1.1 200 OK
< host: swiftinit.org
< link: <https://swiftinit.org/>; rel="canonical"
< etag: "8898806577480f6f7e5241ff270a9201"
< access-control-allow-origin: *
< content-length: 18933
< content-type: text/html; charset=utf-8
<

is there a way i can see the discourse fetch response?