I am using PowerShell and MSGraphAPI to write to SharePoint. I am pulling the user principal name like this:

$AssignedTech = (Get-ADUser $ENV:UserName -Properties userPrincipalName -Server ServerName.mycompany.local | Select UserPrincipalName).UserPrincipalName

This is successfully grabbing the users email address, however when I write to a new entry, all properties are written except for this field. I know I need to somehow lookup the user’s ObjectID but I can’t figure out how to do that.

My code that is writing to SharePoint is as follows.

$params = @{
            fields = @{
                "Title"                            = "$DecomServer";
                "IP_x0020_Address"                 = "$IP";
                "Assigned_x0020_Application"       = "$Application";
                "Domain"                           = "$Domain";
                "Machine_x0020_Type"               = "$MachineType";
                "Change_x0020_Ticket_x0020_Number" = "$ChangeControl";
                "Assigned_x0020_Tech"              = "$AssignedTech";
                "OSVersion"                        = "$OS";
                "DateTurnedOff"                    = Get-Date;
                "RemoveDate"                       = (Get-Date).AddDays(60)
                }
        }
        New-MgSiteListItem -SiteId $siteId -ListId $listId -BodyParameter $params

Can anyone provide some guidance on how to convert the UserprincipalName to the ObjectID needed for a Person or Group field?