Get an Office365 / Azure AD tenant ID from a user’s login name or domain

I often need a tenant ID for a given customer, the usual method to get it is to log in to the Azure portal and find it there. But what if you want to get the tenant ID programmatically? Without actually logging in? And you only know the log in name of a user? Or just one of the customer’s domain names?

Then this’ll help you out!

function get-tenantIdFromLogin(){
    <#
      .SYNOPSIS
      Retrieves an Office 365 / Azure AD tenant ID for a given user login name (email address)
      .EXAMPLE
      $tenantId = get-tenantIdFromLogin -Username you@domain.com
      .PARAMETER Username
      the UPN of a user
      .NOTES
      filename: get-tenantIdFromLogin.ps1
      author: Jos Lieben
      blog: www.lieben.nu
      created: 8/3/2019
    #>
    Param(
        [Parameter(Mandatory=$true)]$Username
    )
    $openIdInfo = Invoke-RestMethod "https://login.windows.net/$($Username.Split("@")[1])/.well-known/openid-configuration" -Method GET
    return $openIdInfo.userinfo_endpoint.Split("/")[3]
}

Obviously, you can also get the tenant ID by just filling out bogus info in front of the user’s login (e.g. bogus@ogd.nl), it’ll still work as only the domain part of the login is really used.

Hope this helps someone 🙂

Git link: https://gitlab.com/Lieben/assortedFunctions/blob/master/get-tenantIdFromLogin.ps1