I don't think this is possible to do on any other domain except extensions.apple.com
.
I've done some extensive testing on this and the safari.installExtension() method is only present if the domain matches extensions.apple.com (probably controlled by the browser, similar to how certain Chrome APIs only shows up inside of extensions themselves).
I tested this theory by going to the JS file itself and opening the JS console:
https://extensions.apple.com/home/scripts/extensionInstall.js
After that JS file has loaded, type typeof(safari.installExtension)
in the JS console and it should return "function"
. Notice that it exists on a non-HTML page, meaning it's being provided by the browser (since this script doesn't execute, nor has the code in it to provide this method).
I tried doing this on other sites and it doesn't exist: "undefined"
.
I also had a crazy thought that it just needs extensions as the subdomain, so I tested it on http://extensions.joomla.org too, no dice. I can't seem to find an extensions sub-domain that's SSL though. That may work, but I seriously doubt it as the method appears to be regulated to only show up when on Apple's specific extensions sub-domain.