Register an app installation for external custom properties

Registers a GitHub App installation so it can read and write external custom properties for an organization, and assigns it a display name.

The display name must be 1 to 15 characters and contain only letters and numbers. Capitalization is preserved as entered.

An app installation can only be registered once, and its display name can't be changed afterward. Calling with an app installation that has already been registered returns a 422 response with an already_exists error code for installation_id. If the display name is already in use by another app installation in the organization, the response is 422 with an already_exists error code for display_name. An invalid display name also returns 422.

The app installation being registered must have write or admin permission for organization external custom properties for repositories. If it doesn't, the response is 422. This is the permission of the installation being registered, which isn't necessarily the caller.

Uninstalling the GitHub App unregisters it, and removes the external custom properties it created.

To use this endpoint, the authenticated caller must have the organization_external_properties_for_repos:admin permission.