The [[https://www.mediawiki.org/wiki/Extension:UrlShortener |UrlShortener extension]] is designed to implement Tim's suggestion from https://www.mediawiki.org/wiki/Requests_for_comment/URL_shortener#Tim.27s_implementation_suggestion
It provides a special page, Special:UrlShortener, that accepts arbitrary links from whitelisted domains, and gives them short urls. It is intended that we will use the "w.wiki" domain for this.
[x] Create a tracking bug for the extension's deployment to Wikimedia wikis. This bug should only concern deployment itself, any sub-issues (that block deployment) should be separate bugs that are listed under "Blocked by" for this tracking bug.
[x] Create Extension: mediawiki.org page for developers and people who will install or configure the extension.
[x] Create Help:Extension: mediawiki.org page for the end user documentation. Cross-link it with the above.
[x] Request a project in Phabricator if none exists yet.
[x] Get the extension code in Gerrit.
[x] Show community support/desire for the extension to be deployed.
 Request (and respond to) a product review, if applicable
 Request (and respond to) a design review, if applicable.
[*] Open (and respond to) a #Security-Reviews ticket blocking this.
[x] Make sure the extension is [[ https://github.com/wikimedia/mediawiki-tools-release | automatically branched ]].
Test at: https://en.wikipedia.beta.wmflabs.org/ ("Get shortened URL" in Toolbox - Beta cluster gives a local "short" domain with e.g. https://w-beta.wmflabs.org/4, hacky setup, but it should work).