Native applications often register themselves as protocol handlers to increase discoverability and usage. It would be great to have PWAs do the same via a new manifest property. The proposal here is for a new optional protocol_handlers property to be added to the manifest.

While websites do currently have this ability via registerProtocolHandler() (which for the most part just registers the browser as the handler to the OS), it would be interesting to have PWAs be first-class citizens and have the option to declare what protocols they want to handle via the manifest. They then would be launched directly when a custom-scheme link is invoked.

Explainer:

https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/master/URLProtocolHandler/explainer.md

Related issue:

It looks like this proposal shares some similarities with #626 (Add a means to associate a PWA with a file extension), and we should probably discuss if they should be unified or kept separate.