Create a new WebExtension API/permission: Provide API to sites

[danfinlay]

At MetaMask, we use the WebExtension "read and write data on all sites you visit" permission for the unusual purpose of providing an additional API to sites a user visits.

A downside of this is that security-conscious users are nervous about approving such all-encompassing permissions, and in fact if our distribution system were compromised, the potential impacts could be large.

Long term, we probably need to be simply integrated into browsers. But medium term, we would greatly benefit from a new WebExtension API & accompanying permission that explicitly only provides an API to sites.

Such a permission would not:

• Allow us to freely read from websites a user visits
• Run keystroke logging on sites a user visits
• Manipulate how a page otherwise loads for a user.

This permission would only:

• Allow us to define an object that could be exposed globally on the window object.
• Allow this object to call back when its methods were called.
• Allow this object to pass methods back to the background process before responding.
• Allow registering listeners for events triggered from the background process.

[BrendanEich]

Dan, thanks for filing. Has anyone tried getting Google's attention on such an API for extensions being added? Thanks.

[danfinlay]

No, I don't think we've filed for Google's attention on this yet, although we did have some discussions with Mozilla a while back:

https://bugzilla.mozilla.org/show_bug.cgi?id=1319168

(Not the exact topic but on the same domain)

[danfinlay]

Another discussion on this topic is here: MetaMask/metamask-extension#813 (comment)

We thought maybe the Component.utils.cloneInto api could be used for this with some adjustments.

[danfinlay]

Actually maybe we need to revisit this on the MetaMask side. Looks like the externally_connectable from sites feature was added so that extensions like MetaMask could do this.

Here's the Chromium discussion on that topic:
https://bugs.chromium.org/p/chromium/issues/detail?id=679238