Today, the “sender” of an Installation creation is only included in the webhook for the “integration_installation” event with the “created” action.
A productive pattern for integrating with webhooks is to not read their data directly – instead using the webhook as a trigger to fetch the corresponding data directly from the Github API. This is particularly useful as a pattern for improving webhook processing reliability, as Github does not retry webhook sends, so any exception in your processing means you’ve lost your chance to process that data.
In turn, it would be convenient for the “integration/installations” endpoint to return the “sender” of the installation as well (https://developer.github.com/v3/integrations/#find-installations).
The sender tends to approximately equal the administrator of the integration, so with this functionality, the “integration_installation” can actually serve as a higher-level authorization handshake for Integrations that also have a web application component.
Thanks for your consideration!