分享更多知识：）

$webRequest = [Net.WebRequest]::Create("https://www.outlook.com")
try { $webRequest.GetResponse() } catch {}
$cert = $webRequest.ServicePoint.Certificate
$bytes = $cert.Export([Security.Cryptography.X509Certificates.X509ContentType]::Cert)
set-content -value $bytes -encoding byte -path "$pwd\Outlook.Com.cer"

我的同事迈克尔·J里昂和我分享了这个。

您应该能够通过使用HttpWebRequest对象上的ServicePoint属性来获取公钥。一旦我们向有问题的网站发出http请求，这些必要的信息将被填充。
如果向具有不受信任证书的站点发出请求，GetResponse方法将抛出异常，但是，ServicePoint仍将包含Certificate，因此我们希望确保在状态为信任失败时忽略WebException。
因此，类似以下的东西应该可以工作：

function Get-PublicKey
{
    [OutputType([byte[]])]
    PARAM (
        [Uri]$Uri
    )

    if (-Not ($uri.Scheme -eq "https"))
    {
        Write-Error "You can only get keys for https addresses"
        return
    }

    $request = [System.Net.HttpWebRequest]::Create($uri)

    try
    {
        #Make the request but ignore (dispose it) the response, since we only care about the service point
        $request.GetResponse().Dispose()
    }
    catch [System.Net.WebException]
    {
        if ($_.Exception.Status -eq [System.Net.WebExceptionStatus]::TrustFailure)
        {
            #We ignore trust failures, since we only want the certificate, and the service point is still populated at this point
        }
        else
        {
            #Let other exceptions bubble up, or write-error the exception and return from this method
            throw
        }
    }

    #The ServicePoint object should now contain the Certificate for the site.
    $servicePoint = $request.ServicePoint
    $key = $servicePoint.Certificate.GetPublicKey()
    Write-Output $key
}

Get-PublicKey -Uri "https://www.bing.com"
Get-PublicKey -Uri "https://www.facebook.com"

如果您想多次调用该方法，并且某些方法可能具有相同的地址，则可能需要使用[ServicePointManager.FindServicePoint(System.Uri)](http://msdn.microsoft.com/en-us/library/c5f0atwd%28v=vs.110%29.aspx)方法来改进该函数，因为如果已向该站点发出请求，则它将返回缓存版本。因此，您可以检查服务点是否已填充信息。如果没有，则发出Web请求。如果有，只需使用已经存在的信息，为自己节省一个http请求。

http://poshcode.org/2521：

function Get-WebsiteCertificate {
  [CmdletBinding()]
  param (
    [Parameter(Mandatory=$true)] [System.Uri]
      $Uri,
    [Parameter()] [System.IO.FileInfo]
      $OutputFile,
    [Parameter()] [Switch]
      $UseSystemProxy,  
    [Parameter()] [Switch]
      $UseDefaultCredentials,
    [Parameter()] [Switch]
      $TrustAllCertificates
  )
  try {
    $request = [System.Net.WebRequest]::Create($Uri)
    if ($UseSystemProxy) {
      $request.Proxy = [System.Net.WebRequest]::DefaultWebProxy
    }

    if ($UseSystemProxy -and $UseDefaultCredentials) {
      $request.Proxy.Credentials = [System.Net.CredentialCache]::DefaultNetworkCredentials
    }

    if ($TrustAllCertificates) {
      # Create a compilation environment
      $Provider=New-Object Microsoft.CSharp.CSharpCodeProvider
      $Compiler=$Provider.CreateCompiler()
      $Params=New-Object System.CodeDom.Compiler.CompilerParameters
      $Params.GenerateExecutable=$False
      $Params.GenerateInMemory=$True
      $Params.IncludeDebugInformation=$False
      $Params.ReferencedAssemblies.Add("System.DLL") > $null
      $TASource=@'
        namespace Local.ToolkitExtensions.Net.CertificatePolicy {
          public class TrustAll : System.Net.ICertificatePolicy {
            public TrustAll() { 
            }
            public bool CheckValidationResult(System.Net.ServicePoint sp,
              System.Security.Cryptography.X509Certificates.X509Certificate cert, 
              System.Net.WebRequest req, int problem) {
              return true;
            }
          }
        }
'@ 
      $TAResults=$Provider.CompileAssemblyFromSource($Params,$TASource)
      $TAAssembly=$TAResults.CompiledAssembly

      ## We now create an instance of the TrustAll and attach it to the ServicePointManager
      $TrustAll=$TAAssembly.CreateInstance("Local.ToolkitExtensions.Net.CertificatePolicy.TrustAll")
      [System.Net.ServicePointManager]::CertificatePolicy=$TrustAll
    }

    $response = $request.GetResponse()
    $servicePoint = $request.ServicePoint
    $certificate = $servicePoint.Certificate

    if ($OutputFile) {
      $certBytes = $certificate.Export(
          [System.Security.Cryptography.X509Certificates.X509ContentType]::Cert
        )
      [System.IO.File]::WriteAllBytes( $OutputFile, $certBytes )
      $OutputFile.Refresh()
      return $OutputFile
    } else {
      return $certificate
    }
  } catch {
    Write-Error "Failed to get website certificate. The error was '$_'."
    return $null
  }

  <#
    .SYNOPSIS
      Retrieves the certificate used by a website.

    .DESCRIPTION
      Retrieves the certificate used by a website. Returns either an object or file.

    .PARAMETER  Uri
      The URL of the website. This should start with https.

    .PARAMETER  OutputFile
      Specifies what file to save the certificate as.

    .PARAMETER  UseSystemProxy
      Whether or not to use the system proxy settings.

    .PARAMETER  UseDefaultCredentials
      Whether or not to use the system logon credentials for the proxy.

    .PARAMETER  TrustAllCertificates
      Ignore certificate errors for certificates that are expired, have a mismatched common name or are self signed.

    .EXAMPLE
      PS C:\> Get-WebsiteCertificate "https://www.gmail.com" -UseSystemProxy -UseDefaultCredentials -TrustAllCertificates -OutputFile C:\gmail.cer

    .INPUTS
      Does not accept pipeline input.

    .OUTPUTS
      System.Security.Cryptography.X509Certificates.X509Certificate, System.IO.FileInfo
  #>
}

function Import-Certificate {
<#
    .SYNOPSIS
        Imports certificate in specified certificate store.

    .DESCRIPTION
        Imports certificate in specified certificate store.

    .PARAMETER  CertFile
        The certificate file to be imported.

    .PARAMETER  StoreNames
        The certificate store(s) in which the certificate should be imported.

    .PARAMETER  LocalMachine
        Using the local machine certificate store to import the certificate

    .PARAMETER  CurrentUser
        Using the current user certificate store to import the certificate

    .PARAMETER  CertPassword
        The password which may be used to protect the certificate file

    .EXAMPLE
        PS C:\> Import-Certificate C:\Temp\myCert.cer

        Imports certificate file myCert.cer into the current users personal store

    .EXAMPLE
        PS C:\> Import-Certificate -CertFile C:\Temp\myCert.cer -StoreNames my

        Imports certificate file myCert.cer into the current users personal store

    .EXAMPLE
        PS C:\> Import-Certificate -Cert $certificate -StoreNames my -StoreType LocalMachine

        Imports the certificate stored in $certificate into the local machines personal store 

    .EXAMPLE
        PS C:\> Import-Certificate -Cert $certificate -SN my -ST Machine

        Imports the certificate stored in $certificate into the local machines personal store using alias names

    .EXAMPLE
        PS C:\> ls cert:\currentUser\TrustedPublisher | Import-Certificate -ST Machine -SN TrustedPublisher

        Copies the certificates found in current users TrustedPublishers store to local machines TrustedPublisher using alias  

    .INPUTS
        System.String|System.Security.Cryptography.X509Certificates.X509Certificate2, System.String, System.String

    .OUTPUTS
        NA

    .NOTES
        NAME:      Import-Certificate
        AUTHOR:    Patrick Sczepanksi (Original anti121)
        VERSION:   20110502
        #Requires -Version 2.0
    .LINK
        http://poshcode.org/2643
        http://poshcode.org/1937 (Link to original script)

#>

    [CmdletBinding()]
    param
    (
        [Parameter(ValueFromPipeline=$true,Mandatory=$true, Position=0, ParameterSetName="CertFile")]
        [System.IO.FileInfo]
        $CertFile,

        [Parameter(ValueFromPipeline=$true,Mandatory=$true, Position=0, ParameterSetName="Cert")]
        [System.Security.Cryptography.X509Certificates.X509Certificate2]
        $Cert,

        [Parameter(Position=1)]
        [Alias("SN")]
        [string[]] $StoreNames = "My",

        [Parameter(Position=2)]
        [Alias("Type","ST")]
        [ValidateSet("LocalMachine","Machine","CurrentUser","User")]
        [string]$StoreType = "CurrentUser",

        [Parameter(Position=3)]
        [Alias("Password","PW")]
        [string] $CertPassword
    )

    begin
    {
        [void][System.Reflection.Assembly]::LoadWithPartialName("System.Security")
    }

    process 
    {
        switch ($pscmdlet.ParameterSetName) {
            "CertFile" {
                try {
                    $Cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2 $($CertFile.FullName),$CertPassword
                }
                catch {   
                    Write-Error ("Error reading '$CertFile': $_ .") -ErrorAction:Continue
                }
            }
            "Cert" {

            }
            default {
                Write-Error "Missing parameter:`nYou need to specify either a certificate or a certificate file name."
            }
        }

        switch -regex ($storeType) {
            "Machine$" { $StoreScope = "LocalMachine" }
            "User$"  { $StoreScope = "CurrentUser" }
        } 

        if ( $Cert ) {
            $StoreNames | ForEach-Object {
                $StoreName = $_
                Write-Verbose " [Import-Certificate] :: $($Cert.Subject) ($($Cert.Thumbprint))"
                Write-Verbose " [Import-Certificate] :: Import into cert:\$StoreScope\$StoreName"

                if (Test-Path "cert:\$StoreScope\$StoreName") {
                    try
                    {
                        $store = New-Object System.Security.Cryptography.X509Certificates.X509Store $StoreName, $StoreScope
                        $store.Open([System.Security.Cryptography.X509Certificates.OpenFlags]::ReadWrite)
                        $store.Add($Cert)
                        if ( $CertFile ) {
                            Write-Verbose " [Import-Certificate] :: Successfully added '$CertFile' to 'cert:\$StoreScope\$StoreName'."
                        } else {
                            Write-Verbose " [Import-Certificate] :: Successfully added '$($Cert.Subject) ($($Cert.Thumbprint))' to 'cert:\$StoreScope\$StoreName'."
                        }
                    }
                    catch
                    {
                        Write-Error ("Error adding '$($Cert.Subject) ($($Cert.Thumbprint))' to 'cert:\$StoreScope\$StoreName': $_ .") -ErrorAction:Continue
                    }
                    if ( $store ) {
                        $store.Close()
                    }
                } 
                else {
                    Write-Warning "Certificate store '$StoreName' does not exist. Skipping..."
                }
            }
        } else {
            Write-Warning "No certificates found."
        }
    }

    end { 
        Write-Host "Finished importing certificates." 
    }
}

我成功地使用了这些功能，如下所示：

##Import self-signed certificate
Get-WebsiteCertificate $baseUrl local.cer -trust | Out-Null
Import-Certificate -certfile local.cer -SN Root  | Out-Null

@RafaMarrara的回答对我来说很完美，有一个澄清：你不能从.NET Core应用程序执行此操作，所以我必须打开PowerShell 5.1才能运行此操作。在PowerShell 7中运行此命令会导致 Certificate 属性始终为空。
原因是.NET Core放弃了对ServicePointManager和ServicePoint类（reference）的支持。