Rewrite "mixed content" URLs via an HTMLPurifier custom filter

[Aaron Wells]

"Mixed content" refers to the scenario where a web page is served via HTTPS, but it includes assets that are served via an HTTP URL. See https://developer.mozilla.org/en-US/docs/Security/Mixed_content for some discussion of this.

In Bug 1463629 we fixed this issue for embedded iframes, by patching the HTMLPurifier core class HTMLPurifier_URIFilter_SafeIframe so that, in addition to filtering iframes for an allowed set of URLs, it also transformed them from HTTPS to HTTP if needed.

After having recently done some work on HTMLPurifier for other bugs, and becoming more familiar with their API, it now becomes apparent to me that this was a bit of a hack (patching core code should have told me this anyway). What we should have done is, instead, write up a new custom URIFilter specifically for rewriting URI's from HTTP to HTTPS in this way, and used that instead.

Doing it that way will make future HTMLPurifier upgrades easier, by eliminating the need to patch that file.

[Aaron Wells (u-aaronw)]

See http://htmlpurifier.org/docs/enduser-uri-filter.html for details about how to write a custom URI filter.

[Kristina Hoeppner (kris-hoeppner)]

To be revisited when we upgrade HTMLpurifier for 19.04

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/9625

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/9625
Committed: https://git.mahara.org/mahara/mahara/commit/49d1c1b9a75c07fccaa12bcb31ed34f5f0ec3f3a
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit 49d1c1b9a75c07fccaa12bcb31ed34f5f0ec3f3a
Author: Cecilia Vela Gurovic <email address hidden>
Date: Wed Mar 13 15:50:36 2019 +1300

Bug 1563641: "mixed content" URLs via an HTMLPurifier custom filter

behatnotneeded

Change-Id: I8c3b5facad985b997848f93a50398a397922f4af

[Mahara Bot (dev-mahara)]

Patch for "19.04_STABLE" branch: https://reviews.mahara.org/9708

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/9708
Committed: https://git.mahara.org/mahara/mahara/commit/81830c5edffeb1d9d21af72442d60e1c55eb74c6
Submitter: Robert Lyon (<email address hidden>)
Branch: 19.04_STABLE

commit 81830c5edffeb1d9d21af72442d60e1c55eb74c6
Author: Cecilia Vela Gurovic <email address hidden>
Date: Wed Mar 13 15:50:36 2019 +1300

Bug 1563641: "mixed content" URLs via an HTMLPurifier custom filter

behatnotneeded

Change-Id: I8c3b5facad985b997848f93a50398a397922f4af
(cherry picked from commit 49d1c1b9a75c07fccaa12bcb31ed34f5f0ec3f3a)