Script a new connection

The Power BI API does not support ServicePrincipal as the credentialType. You will have to use the Fabric API instead.

You will also have to encrypt the Service Principal credentials. This can be done as follows (using the pre-release v5 version of the Microsoft.PowerBI.API library - unfortunately no helper class exists for ServicePrincipal so doing this manually instead):

$credentialData = @{
        credentialData = @(
            @{
                name = "tenantId"
                value = $tenantId
            },
            @{
                name = "servicePrincipalClientId"
                value = $clientId
            },
            @{
                name = "servicePrincipalSecret"
                value = $secret
            }
            )
        } | ConvertTo-Json -Depth 3

    $gatewayKeyObject = [Microsoft.PowerBI.Api.Models.MicrosoftPowerBIApiModelFactory]::GatewayPublicKey($gatewayExponent, $gatewayModulus)
    $credentialsEncryptor = [Microsoft.PowerBI.Api.Extensions.AsymmetricKeyEncryptor]::new($gatewayKeyObject)
    $spnCreds = $CredentialsEncryptor.EncodeCredentials($credentialData)

    $credentialDetails = @{
        singleSignOnType = "None"
        connectionEncryption = "Any"
        skipTestConnection = $true
        credentials = @{
            credentialType = "ServicePrincipal"
            values = @(
                @{
                    gatewayId = $gatewayId
                    encryptedCredentials = $spnCreds
                }
            )
        }
    }