Accessing G Suite Admin SDK using service account

Question

I am trying to use a service account to access Directory API (https://developers.google.com/admin-sdk/directory/v1/reference/users/list). The simplest task is to list users in the organization. That works well with my user account, tested with the OAuth 2.0 Playgorund. But I need to use service account. I am following documentation for two-legged OAuth (https://developers.google.com/identity/protocols/OAuth2ServiceAccount) and implementing REST client in Powershell

• API Access enabled in Google Admin Console
• The service acount is created and P12 credentials downloaded. The account is granted several organization-wide roles in Cloud Console: Browser, Security Reviewer, Organization Viewer - so as to test various scenarios
• Domain-wide authority is granted in the Admin Console, with API scope https://www.googleapis.com/auth/admin.directory.user

Powershell code:

    # Forming the JWT claim set

    $cert = Get-PfxCertificate -FilePath "c:\ps\GAdmin\apiaccess-123456.p12" -Password (ConvertTo-SecureString "notasecret" -AsPlainText -Force)

    $now = (Get-Date).ToUniversalTime()
    $createDate = [Math]::Floor([decimal](Get-Date($now) -UFormat "%s"))
    $expiryDate = [Math]::Floor([decimal](Get-Date($now.AddHours(1)) -UFormat "%s"))

    $rawclaims = [Ordered]@{
            iss = "p12service@apiaccess-123456.iam.gserviceaccount.com"
            scope = "https://www.googleapis.com/auth/admin.directory.user"
            aud = "https://www.googleapis.com/oauth2/v4/token"
            iat = $createDate
            exp = $expiryDate
    } | ConvertTo-Json

    # Encoding the JWT claim set

    $jwt = New-Jwt -PayloadJson $rawclaims -Cert $cert -Verbose

    # Making the access token request

    $apiendpoint = "https://www.googleapis.com/oauth2/v4/token"

    $splat = @{
            Method = "POST"
            Uri = $apiendpoint
            ContentType = "application/x-www-form-urlencoded"
            Body = "grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer&assertion=$jwt"
    }

    $res = Invoke-WebRequest @splat -Verbose

    $accesstoken = ($res.content | ConvertFrom-Json).access_token

    # Calling Google APIs - list of users

    $usersapiendpoint = "https://www.googleapis.com/admin/directory/v1/users?list&customer=my_customer&domain=mydomain.com.au"

    $splat = @{
            Method = "GET"
            Uri = $usersapiendpoint
            Headers = @{authorization = "Bearer $accesstoken"}
    }

    $userlistres = Invoke-WebRequest @splat -Verbose

This results in error:

code 403, "Not Authorized to access this resource/api"

Calling other APIs works. What do I need to do to enable programmatic access to the Directory API? Am I missing a configuration step for the service account/SDK access?

Answer 1

Got this working! The domain-wide authority delegation and impersonation (a sub = "user@example.com" entry in the $rawclaims) were necessary and correct.

The problem was that there was a mismatch between the privileges granted to the service account through the domain-wide delegation, and those requested in my claim (I had several):

scope = "https://www.googleapis.com/auth/admin.directory.user https://www.googleapis.com/auth/iam https://www.googleapis.com/auth/cloud-platform"

Once claims matched granted privileges, I received my tokens.