I had a hard time finding the information I needed to get Cockpit to work right behind an Apache reverse proxy setup. So, I decided to collect everything I found here for the future.
At first, I tried to setup cockpit under the /cockpit path but it kept failing. Apparently, that path is reserved by Cockpit, so I switched to using /ckpt/ instead.
/etc/cockpit/cockpit.conf
[WebService]
Origins = https://mydomain.com http://127.0.0.1:9090
ProtocolHeader = X-Forwarded-Proto
AllowUnencrypted = true
UrlRoot = /ckpt/
ProxyPreserveHost On
ProxyRequests Off
SSLProxyVerify None
SSLProxyCheckPeerCN Off
SSLProxyCheckPeerName Off
SSLProxyCheckPeerExpire Off
RewriteEngine On
RewriteCond %{HTTP:Upgrade} =websocket [NC]
RewriteRule /ckpt/(.*) ws://127.0.0.1:9090/ckpt/$1 [P,L]
RewriteCond %{HTTP:Upgrade} !=websocket [NC]
RewriteRule /ckpt/(.*) http://127.0.0.1:9090/ckpt/$1 [P,L]
ProxyPass /ckpt/ http://127.0.0.1:9090/ckpt/
ProxyPassReverse /ckpt/ http://127.0.0.1:9090/ckpt/