Add Microsoft provider

[MicheleIRDG]

Describe the feature you would like to see

Hi
I have a firebase user created with mail
i need to allow that user ti log-in with microsoft...

is there a function for link new provider to the user?
i have see that "$signInResult = $auth->signInWithIdpAccessToken($provider, $accessToken, $redirectUrl = null, $oauthTokenSecret = null, $linkingIdToken);" but i don't understand how use it in this casecan i have a little demo?