Access Shared Mailboxes

This wasn't covered in the examples when I needed it, so I writing an entry for the next person. Below is the init function for a class I wrote. When I needed to deal with Shared Mailboxes I was stuck in how to access them. The solution required four changes

1. Create an access token for an account that has access to the shared mailbox. You can't connect to a shared mailbox directly.
2. Your scopes need to be expanded to include Shared permission. i.e. ReadWrite.Shared
3. Your API permissions for your app in Azure must grant the Shared permissions
4. You need to include the main_resource=some_shared_email@somewhere.org keyword in you initial call to Account

    def __init__(self, app_data: ApplicationData):
        """Perform initialization steps"""
        credentials = (app_data.app_id, app_data.secret)
        # the default protocol will be Microsoft Graph
        # the default authentication method will be "on behalf of a user"
        self.scopes = [
            "https://graph.microsoft.com/Mail.ReadWrite",
            "https://graph.microsoft.com/Mail.Send",
            "https://graph.microsoft.com/Mail.ReadWrite.Shared",
            "https://graph.microsoft.com/Mail.Send.Shared",
            "offline_access",
        ]

        # Set up token storage and retrieval
        token_backend = FileSystemTokenBackend(
            token_path=app_data.tokenpath, token_filename=app_data.token
        )
        # Set up Account connection
        self.account = Account(
            credentials,
            main_resource=app_data.main_resource,
            tenant_id=app_data.tenant,
            auth_flow_type="authorization",
            scopes=self.scopes,
            token_backend=token_backend,

        )
        # Check status.  Is_authenticated will load token and request a refresh,  if that fails
        # the account is authenticated again and the user has to grant permissions.
        if not self.account.is_authenticated:
            if self.account.authenticate():
                print("Authenticated!")
                # This forces the generation of a refresh token which is good for 90 days
                self.account.connection.refresh_token()
        # Connect to the mailbox, then to the inbox folder.
        self.count = 0
        self.mailbox = self.account.mailbox()