[Web Install] How can install targets advertise a preferred `install_url`?

[amandabaker]

https://bit.ly/unvalidated-pwa-url-installation describes the benefits of having a dedicated install url that is lightweight, doesn't redirect, and only includes the resources needed to install the app. Large app stores may have a registration process that requests a specific install url, but smaller players may rely on web crawlers to find apps to host in their store.

A failed or slow app install (due to redirects or loading too many resources over a slow connection) reflects poorly on both the store (install source) and app (install target), so it's beneficial to both parties that there is an easy way for the installation target to specify a preferred install url.

Proposal: Add an install_url field to the manifest:

• Pro: If stores are already using crawlers to find available PWAs and their specified manifest_ids, then checking the install_url would be a trivial addition.
• Con: There is no precedence for adding a field to the manifest that is not used by the browser.

cc @dmurph @diekus @HowardWolosky

[dmurph]

I'm generally in support of this, I think it is useful. It also help admin / policy install situations, where the admin panel can look at the manifest & see the install_url, and then populate that in the policy sent to the client along with the manifest_id.

[diekus]

I am supportive of this as well. Need to add this to the manifest incubations spec.