Microsoft Login Screen
Hosts the Microsoft login page in a CEF browser.
MinecraftAuth ships a JavaFX web view for this, but we do not ship JavaFX, so ExternalBrowserMsaAuthService lets the login run in the browser the client already has. The screen reports every URL the page navigates to, and the service picks the auth code out of the redirect.
The browser is incognito, so the Microsoft session never reaches the client's cookie store. Without that, signing in would leave the account logged in for anyone who opens a browser afterwards, and adding a second account would silently reuse the first one's session instead of asking who to sign in as.
The screen does not close itself on success - the service's close callback does, once the auth code has been exchanged for a token.