Confirmed Microsoft connected account registration fails with missing provider_key

[eric990]

Affected version

2.3.12

When attempting to use the built-in Microsoft connected account provider, authentication with Microsoft completes successfully, but XenForo fails after redirecting back with:

Oops! We ran into some problems.
Please enter a value for the required field 'provider_key'.

The ACP 'Test provider' function similarly reports:

Test failed while connecting with Microsoft. Unable to retrieve provider key.

I was able to reproduce on several prominent XenForo boards. Seems Microsoft may have changed what it passes back?