Set-PSUAuthenticationMethod -Type "Form" -ScriptBlock {
param(
    [PSCredential]$Credential
)

#
#   You can call whatever cmdlets you like to conduct authentication here.
#   Just make sure to return the $Result with the Success property set to $true
#
$Result = [Security.AuthenticationResult]::new()
if ($Credential.UserName -eq 'Admin' -and $Credential.GetNetworkCredential().password -eq "PASSWORD")
{
    #Maintain the out of box admin user
    $Result.UserName = 'Default Admin'
    $Result.Success = $true
}
else
{
    # Get current domain using logged-on user's credentials - this validates their credential
    $CurrentDomain = "LDAP://DC=domain,DC=local"  # Insert Your Domain Here
    $domain = New-Object System.DirectoryServices.DirectoryEntry($CurrentDomain,($Credential.UserName),$Credential.GetNetworkCredential().password)
    if ($domain.name -eq $null)
    {
        #"Authentication failed for $($Credential.UserName)!"
        write-host "Authentication failed - please verify your username and password."
        $Result.UserName = ($Credential.UserName)
        $Result.Success = $false
    }
    else
    {
        write-host "Successfully authenticated with domain $($domain.name)"
        #"Authentication success for $($Credential.UserName)!"
        $groupMember = Get-ADGroupMember -Identity GROUPNAME -Recursive | select-object -ExpandProperty samaccountname
        if ($groupMember -contains $credential.UserName){
            $Result.UserName = ($Credential.UserName)
            $Result.Success = $true
        }
        else {
            $Result.UserName = ($Credential.UserName)
            $Result.Success = $false
        }
    }
}

$Result
} -SaveTokens $false -UseTokenLifetime $false -GetClaimsFromUserInfoEndpoint $false