@tsuji_koichi We have had reports of users getting stuck in a sign-in loop with Office 365 or OneDrive. These incidents appear to be intermittent and usually do not last. We are still looking into this.
Regarding my earlier comment about signing into an app that uses data from Google with an Office 365 account, I believe I was giving you incorrect information. Here’s the correct answer: each table in your app has a setting called “Access mode”, which can be toggled between “as app creator” or “as app user”. When the app user accesses the table’s data as the app creator, they will use your own Google credentials to access spreadsheets in your own GDrive. In other words, you are “lending” them your credentials so that they can view and work on your data on your behalf. That’s why it’s possible for your users to sign into your app using Office 365 accounts even though your app uses data from Google.
However, if the app user accesses the app’s data as themselves (as app user), they will need to use their own credentials, which means that you must either share your spreadsheets with them directly, or they must be the owner of the spreadsheet. In this case, because the user must have direct access to the spreadsheet, they must sign in using a Google account in order to use the app.