title: Microsoft Graph API - "Error authenticating with resource" 400s on calendar endpoints
body: <p>Have an application that uses the Graph API to access calendar data for users using outlook.com and office365. Integration has been live for months and working properly, but recently we've started receiving 400 "Error authenticating with resource" responses when attempting to fetch the users calendars (/me/calendars). Access tokens are not expired and our app requests the correct scopes during signup (User.Read Calendars.ReadWrite offline_access). Would appreciate any help on getting this resolved.</p>