Hi @MikeTang,
Actually I think PowerApps Studio is using the token to access all the available connections, such as OneDrive for Business, SharePoint Online and Office 365 Outlook.
I will explain how PowerApps work with the data sources. Hope this would make it clear.
For now, PowerApps uses connections to work with data source. For different data source, such as SharePoint, OneDrive or SQL Server, and other online services, the authentication information would be kept in the connection 'object'.
Check the article below for more information about connections:
Manage your connections in PowerApps
If you have signed in PowerApps with the Office 365 Account, when adding new connections for the data source which are involved in the Office 365 plan, it will not need to enter the authentication information again under PowerApps studio.
Besides, if multiple authentication infomartion have been added, it will then require you to choose one.
Regards,
Michael