Check for expiring SSL certificates

Get-SSLCertificateDates

# Written for Powershell 5.1
function Get-SSLCertificateDates {
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [String]
        $URL
    )
    [Net.ServicePointManager]::ServerCertificateValidationCallback = { $true }
    $req = [Net.HttpWebRequest]::Create($URL)
    try {
        $req.GetResponse() | Out-Null
    }
    catch {}
    $cert = [PSCustomObject]@{
        URL = $URL
        'CertStartDate' = $req.ServicePoint.Certificate.GetEffectiveDateString()
        'CertEndDate' = $req.ServicePoint.Certificate.GetExpirationDateString()
    }
    $cert
}

$urls = @()
$urls += "https://www.microsoft.com"
$urls += "https://www.google.com"
$urls += "https://expired.badssl.com"

foreach ($url in $urls) {
    $SSLCertificateDates = Get-SSLCertificateDates -URL $url

    $today = Get-Date
    $certWarnDate = (Get-Date $($SSLCertificateDates.CertEndDate)).AddDays(-90)
    if ($today -gt $certWarnDate) {
        "Certificate warning for $url, expiring on $($SSLCertificateDates.CertEndDate)."
    }
}