A normal Microsoft sign-in with your Vestey account — only the last step is done by hand, until single sign-on is enabled for this site.
1. Sign in with Microsoft
Open Microsoft sign-inOpens a new tab. You will end on a blank page — that is expected.
2. Copy that blank page's address
Click the address bar, select all, copy. It contains ?code=, e.g. https://login.live.com/oauth20_desktop.srf?code=…
3. Paste it here