Add Filter to fix mixed content warnings on WordCamp Sites

[BandonRandon]

Now that all WordCamp sites were switched to force SSL with certificates from Lets Encrypt some sites are showing mixed content warnings.

These warnings are more likely to happen on older WordCamp sites that were created before switching everything over to SSL. For example:
​https://2014.seattle.wordcamp.org/

Instead of asking organizers to go back and fix these sites, we could instead add filters of either the_content or the site's buffer to force all content to be loaded from https URLs.

Potential downside would be linked images from http sources which don't support https. If a site has Jetpack, Photon should be able to rectify these situations.

[BandonRandon]

Mixed Content warning of 2014.seattle.wordcamp.org in Brave

[iandunn]

+1

linked images from http sources which don't support https

I think we should consider only modifying links that we know support HTTPS, to avoid breaking content. Mixed content warnings are bad, not not as bad as broken images.

[dd32]

I think we should consider only modifying links that we know support HTTPS, to avoid breaking content.

The other option would be to proxy all other http-image assets through Jetpack Photon to utilise it's SSL.

[iandunn]

Replying to dd32:

The other option would be to proxy all other http-image assets through Jetpack Photon to utilise it's SSL.

Ah, +1. I bet that's what Brooke meant in the ticket description, and I just misunderstood it.

[iandunn]

Related #2466

[coreymckrill]

This doesn't seem like something that will ever be a high enough priority that it will get addressed, since it only affects really old sites.