Powershell Connect-MsolService fails to authenticate with Microsoft Graph access token

Hi,

I am trying to authenticate with the MSOnline powershell module using Connect-MsolService. I obtain a user's access token via a web application using the Azure AD Graph (graph.windows.net). If I authenticate with that token (Connect-MsolService -AccessToken <token>), things work fine.

However, since it's recommended to use the newer Microsoft Graph (graph.microsoft.com) I want to switch over to it, but the Connect-MsolService fails with the token granted by it. If I run Connect-MsolService -MsGraphAccessToken <token>, I get the following error: 

Connect-MsolService : The given key was not present in the dictionary.

To obtain the access token, I send users to the https://login.windows.net/common/oauth2/authorize end point with the correct client id, redirect_uri and resource set to https://graph.microsoft.com. The authentication succeeds and I get a valid token back (for example, a request to https://graph.microsoft.com/v1.0/me works fine). 

What am I doing wrong here?

Thanks for your help!

Best,
Steven