connect-pnpmicrosoftgraph Has Been Deprecated

I have a script that creates an Office 365 group and the associated SharePoint site using PnP PowerShell. I recently updated the SharePointPnPPowerShell assemblies to version 2.20.1711.0. Now I'm getting a warning that connect-pnpmicrosoftgraph has been deprecated and will be removed in April 2018.

I have found that connect-pnponline is it's replacement but I'm having trouble connecting. For connect-pnpmicrosoftgraph, I'm using

$conn = connect-pnpmicrosoftgraph -AppId $appid -AppSecret $client_secret -AADDomain "mydomain.onmicrosoft.com" -Verbose;

When I look at the details of Connect-PnPOnline with Microsoft Graph using Azure Active Directory, I see the same parameters, but running this throws an error

connect-pnponline : Value cannot be null.
Parameter name: uriString
At line:1 char:9
+ $conn = connect-pnponline -AppId $appid -AppSecret $client_secret -AA ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Connect-PnPOnline], ArgumentNullException
+ FullyQualifiedErrorId : System.ArgumentNullException,SharePointPnP.PowerShell.Commands.Base.ConnectOnline

Upon further investigation, it appears that AADDomain is incorrect and that I should be using url. But I'm at a loss as to what I'm supposed to use here. I've tried mydomain.onmicrosoft.com, but get an error

Connect-PnPOnline : Invalid URI: The format of the URI could not be determined.
At line:1 char:1
+ Connect-PnPOnline -url "mydomain.onmicrosoft.com" -AppId "xxxxxxx-xxx ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Connect-PnPOnline], UriFormatException
    + FullyQualifiedErrorId : System.UriFormatException,SharePointPnP.PowerShell.Commands.Base.ConnectOnline

So I tried https://mydomain.onmicrosoft.com, but get this error

Connect-PnPOnline : Token request failed.
At line:1 char:1
+ Connect-PnPOnline -url "https://mydomain.onmicrosoft.com" -AppId "xxxx ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Connect-PnPOnline], RequestFailedException
    + FullyQualifiedErrorId : Microsoft.IdentityModel.SecurityTokenService.RequestFailedException,SharePointPnP.PowerShell.Commands.Base.Conne 
   ctOnline

Same when I use https://graph.microsoft.com, and https://mydomain-admin.sharepoint.com

Using https://mydomain.sharepoint.com gives me a 403 forbidden error.

What is the correct replacement URL for connect-pnpmicrosoftgraph?