Support Oauth2 'Client Credentials Flow' for server apps.
Major drawback of Xero Oauth2 is that the 'Client Credentials Flow' is not supported. This makes it impossible to implement server-side applications to interact with Xero because there is no user interaction at all. Lot of people have been complaining about this, and it's shocking that it is still not supported in May 2021!
You can now integrate with client credentials using Custom Connections.