I looked into this issue and this is because Overwatch Forum is returning different headers when making HEAD request (instead of GET).
➜ ~ curl -I https://us.battle.net/forums/en/overwatch/topic/20758326009
HTTP/1.1 302 Found
Date: Fri, 04 Aug 2017 13:57:32 GMT
Server: Apache
X-Frame-Options: SAMEORIGIN
Retry-After: 600
Set-Cookie: login.cookies=1; Domain=battle.net; Path=/
Location: https://us.battle.net/forums/
Content-Language: en-US
➜ ~ curl -I https://us.battle.net/forums/
HTTP/1.1 302 Found
Date: Fri, 04 Aug 2017 13:57:47 GMT
Server: Apache
X-Frame-Options: SAMEORIGIN
Retry-After: 600
Set-Cookie: login.cookies=1; Domain=battle.net; Path=/
Location: https://us.battle.net/forums/en/
➜ ~ curl -I https://us.battle.net/forums/en/
HTTP/1.1 200 OK
Date: Fri, 04 Aug 2017 13:58:08 GMT
Server: Apache
X-Frame-Options: SAMEORIGIN
Retry-After: 600
Set-Cookie: login.cookies=1; Domain=battle.net; Path=/
Content-Language: en-US
Content-Length: 100225
Content-Type: application/xhtml+xml;charset=UTF-8
Since Onebox is making HEAD request to resolve the URL before actually oneboxing it, the final URL is different than provided.
Changing FinalDestination library to make GET request (instead of HEAD) fixes this issue, but I am not sure if that is the correct approach here (since we don’t need the response body in FinalDestination library). What do you think @eviltrout?