Building a trust between Azure instance and local AD

We have an Azure instance that handles credentials for Office 365 that doesn't match our local AD database, but now I need to be able to authenticate to Azure with my Apple products. (Apple School Manager) I don't want to overwrite either instance. Is there a way to build a trust so that my users can remotely authenticate to the local AD? Also the local is a non-routable (.lan) domain.

Any help would be greatly appreciated.