IAdmUsernameDomainSelectionOptions

[Reflection.Assembly]::LoadWithPartialName("Softerra.Adaxes.Adsi")

# Connect to the Adaxes service.
$ns = New-Object "Softerra.Adaxes.Adsi.AdmNamespace"
$service = $ns.GetServiceDirectly("localhost")

# Build the ADS path of the User property pattern and bind to it.
$containerPath = $service.Backend.GetConfigurationContainerPath("PropertyPatterns")
$propertyPatternsPathObj = New-Object "Softerra.Adaxes.Adsi.AdsPath" $containerPath
$builtinPathObj = $propertyPatternsPathObj.CreateChildPath("CN=Builtin")
$userPatternPath = $builtinPathObj.CreateChildPath("CN=User")

$pattern = $service.OpenObject($userPatternPath.ToString(), $null, $null, 0)

# Get the item for the Username property.
foreach ($item in $pattern.Items)
{
    if ($item.PropertyName -ieq "userPrincipalName")
    {
        # Create suffix restrictions for domain.
        $domainRestriction = 
            New-Object Softerra.Adaxes.Adsi.PropertyPatterns.UsernameDomainSelectionOptions
        $domainRestriction.Mode = "HideSpecific"
        $domainRestriction.SpecificDomains = @("example1.com", "example.onmicrosoft.com")
        $domainRestriction.DefaultDomain = "example.com"

        # Set restrictions.
        $domainOptions = New-Object Softerra.Adaxes.Adsi.Utils.AdmKeyValuePair
        $domainOptions.Key = "example.com"
        $domainOptions.Value = $domainRestriction
        $item.DomainOptions += $domainOptions

        $item.SetInfo()
    }
}

using System;
using Softerra.Adaxes.Adsi;
using Softerra.Adaxes.Interop.Adsi.PersistentObjects;
using Softerra.Adaxes.Interop.Adsi.PropertyPatterns;
class Program
{
    static void Main(string[] args)
    {
        // Connect to the Adaxes service.
        AdmNamespace ns = new AdmNamespace();
        IAdmService service = ns.GetServiceDirectly("localhost");

        // Build the ADS path of the User property pattern and bind to it.
        string containerPath = service.Backend.GetConfigurationContainerPath("PropertyPatterns");
        AdsPath propertyPatternsPathObj = new AdsPath(containerPath);
        AdsPath builtinPathObj = propertyPatternsPathObj.CreateChildPath("CN=Builtin");
        AdsPath userPatternPath = builtinPathObj.CreateChildPath("CN=User");

        IAdmPropertyPattern pattern = (IAdmPropertyPattern)service.OpenObject(
            userPatternPath.ToString(), null, null, 0);

        // Get the item for the Username property.
        foreach (IAdmPropertyPatternItem item in pattern.Items)
        {
            if (StringComparer.OrdinalIgnoreCase.Equals("userPrincipalName", item.PropertyName))
            {
                IAdmUsernamePropertyPatternItem usernameItem = (IAdmUsernamePropertyPatternItem)item;

                // Create suffix restrictions for the domain.
                IAdmUsernameDomainSelectionOptions domainRestriction = 
                new UsernameDomainSelectionOptions
                {
                    Mode = UsernameDomainSelectionMode.HideSpecific,
                    SpecificDomains = new[] { "example1.com", "example.onmicrosoft.com" },
                    DefaultDomain = "example.com"
                };

                // Set restrictions.
                IAdmKeyValuePair domainOptions = new AdmKeyValuePair
                {
                    Key = "example.com",
                    Value = domainRestriction
                };
                usernameItem.DomainOptions = new [] { domainOptions };

                usernameItem.SetInfo();
            }
        }
    }
}