For users whose Jira is hosted behind a firewall/proxy, and they are unable to expose the internal URL, Github apps will get stuck in 'Installing' status due to the installation completion webhooks not reaching the intended internal (private) endpoint.

As a work around, some clients have been able to successfully setup external facing proxy URL's to capture the webhooks and forward them to the correct internal endpoint to complete the installation.

In this workflow, the webhook URL from the Github App must be retrieved on the GH side of things after the app has been authenticated, then the proxy is configured to redirect to this (original) internal endpoint. Once that is done, the GH app webhook must be modified to point to the proxy URL, and then the webhooks must be resent to complete the installation.

For clients like these, it would be extremely helpful to have an advanced settings field that would allow them to specify a different proxy URL domain, which will be passed in the GH App manifest instead of the internal domain.

This way, the clients will not have to manually go and grab the webhook URL and then point the proxy to the original URL. The Proxy can be setup to route the external domain URLs to the internal domain endpoints. In the proposed workflow, the GH app will be created with the proxy URL, and the webhooks should be delivered to the to the internal address without any manual modifications to anything.