Emphasis being on "embrace" at this point. It's too early to cry wolf yet -- there's not even an obvious way to get from here to "extend".
In fact, what has MS actually extinguiushed?
https://msdn.microsoft.com/en-us/openspecifications/default
Their kerberos implementation works with heimdal and mit. They used an optinal field to include group membership data so that authorization decisions could be made from the contents of the ticket.
https://msdn.microsoft.com/en-us/library/gg604662.aspx
I'm just saying. Times have changed. Will they ever be as open as an open source project run by volunteers? No. Have they dramatically improved their position in response to the very real criticisms of their past behavior. Yes.
The ASP.NET and other .NET teams beg to differ. Their code (not some mirror) is hosted on Github and Apache licensed. You can fork it just like any other open source project.
So yes, parts of Microsoft's tech is actually free and open, for all practical definitions of free and open (the GNU people's pedantic arguments about Apache not withstanding)
The ASP.net team is kicking major ass.
Wrong. It's too late to automatically assume they've changed their game. They have been making some impressive moves lately, but that doesn't mean they're suddenly trustworthy.
there's not even an obvious way to get from here to "extend"
just look at all the nonstandard SSH authentication methods that exist across networking devices.