I have been using app credentials to access SharePoint via Microsoft's .NET libraries for years. I have joined a new organization that refused to do so, so they added a new user without an inbox to our Azure AD tenant and called it a service account. It shows up in our SharePoint access management, so I gave it access to the necessary files and everything looked great.
However,
The user has no inbox, so I'm not sure if that impacts logging in, but using the
SharePointOnlineCredentialsclass results in an error stating that the credentials aren't valid.I can't even verify if any of these programmatic methods of accessing the files would work with my own account as we have MFA enabled, so logging in with my own username and password programmatically does not work.
Is there anything that can be done to authenticate into our tenant in Azure with this inbox-less account that does show up as a valid user in the system?