Auto-upgrade passive mixed content using a content blocker

[kylehickinson]

Description:

Security review https://github.com/brave/reviews/issues/1488

iOS/WebKit only auto-upgrades active mixed content such as scripts, but we should also add a content blocker to auto-upgrade passive content such as images as per https://www.w3.org/TR/mixed-content/#upgrade-algorithm

The content blocker rule in question:

{
  "trigger": {
    "url-filter": "http://.*",
    "if-top-url": ["https://.*"],
    "resource-type": [
      "image", "media"
    ]
  },
  "action": {
    "type": "make-https"
  }
}

[diracdeltas]

Note that if the content cannot be upgraded (ex: doesn't support HTTPS) it should be blocked from loading

[kylehickinson]

@diracdeltas Can you elaborate? Content blockers only give us so much control, the above will simply make http images, videos and audio URLs load on https and we won't know prior if they actually support https. Those loads would still happen but just fail with some error (likely 404)

[diracdeltas]

@diracdeltas Can you elaborate? Content blockers only give us so much control, the above will simply make http images, videos and audio URLs load on https and we won't know prior if they actually support https. Those loads would still happen but just fail with some error (likely 404)

It's fine if they don't support HTTPS; the important thing is that they don't load over HTTP if the HTTPS redirect fails.