What ways are there to connect an Azure Active Directory app to an external SharePoint site to create and edit files using C#, the SharePoint site must not be in the same AAD account or tenant as the APP
  To connect an Azure Active Directory (AAD) app to an external SharePoint site that is not in the same AAD account or tenant as the app, you can use the SharePoint REST API and the Microsoft Graph API. Here are the general steps you can follow:

1. Register the app in the Azure portal:
	* Go to the Azure portal (<https://portal.azure.com>) and sign in with an account that has admin privileges for the AAD account or tenant where the app will be registered.
	* Search for "Azure Active Directory" in the Azure portal search bar, and then click on "Azure Active Directory" in the search results.
	* Click on "App registrations" in the left navigation menu, and then click on "New registration".
	* Fill in the required information for the app, including the name, redirect URI, and the AAD account or tenant where the app will be registered.
	* Click on "Create" to register the app.
2. Obtain the client ID and client secret:
	* After registering the app, you will be able to obtain the client ID and client secret for the app. You can find these in the "Overview" section of the app registration page in the Azure portal.
	* The client ID is the unique identifier for the app, and the client secret is a password that is used to authenticate
There are two ways to connect an Azure Active Directory app to an external SharePoint site to create and edit files. The first option is to use the SharePoint Client Library for Office 365. This library allows the app to authenticate with the SharePoint site and access files. The second option is to use the SharePoint REST API. This API allows the app to access and manipulate files in the SharePoint site programmatically. The app must not be in the same AAD account or tenant as the SharePoint site in order to connect to it.