Invoke-WebRequest $url -OutFile $path_to_file

Если возникнет ошибка "…Could not create SSL/TLS secure channel." То вести комманду

[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}  

Или один раз выполнить и больше ошибки не будет

Set-ItemProperty -Path 'HKLM:\SOFTWARE\Wow6432Node\Microsoft\.NetFramework\v4.0.30319' -Name 'SchUseStrongCrypto' -Value '1' -Type DWord
Set-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\.NetFramework\v4.0.30319' -Name 'SchUseStrongCrypto' -Value '1' -Type DWord

Invoke-RestMethod $url -OutFile $path_to_file

This method is a wrapper around Invoke-WebRequest, but provides some additional formatting of JSON results. (See documentation here and here.)

  (New-Object System.Net.WebClient).DownloadFile($url, $path_to_file)

  Import-Module BitsTransfer
  Start-BitsTransfer -Source $url -Destination $path_to_file

$webRequest = [Net.WebRequest]::Create("https://www.myserver.ru/")
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls11
[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}
$webRequest.Proxy = $null
$webRequest.GetResponse() 
$cert = $webRequest.ServicePoint.Certificate
$bytes = $cert.Export([Security.Cryptography.X509Certificates.X509ContentType]::Cert)
set-content -value $bytes -encoding byte -path "$pwd\mycert.cer"

При использовании Invoke-RestMethod или Invoke-WebRequest с https на URL сервера, где установлен самоподписанный сертификат, возникали ошибки:

• The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.
• The underlying connection was closed: An unexpected error occurred on a send.

Получилась аж вот такая конструкция, но я нашёл свойство, отключающее проверку сертификата (выделил ):

$URi = "https://<URL>"
$request = [System.Net.WebRequest]::Create($URi)
$data = (New-Object PSObject |
    Add-Member -PassThru NoteProperty user "<USER>" |
    Add-Member -PassThru NoteProperty password "<PASSWORD>"
) | ConvertTo-JSON
$request.KeepAlive = $false
$request.Headers.Add($HeadersCollection)
$request.ContentType = "application/json"
$request.Accept = "application/json"
$request.Method = "POST"
$request.ServerCertificateValidationCallback = {$true} 
$bytes = [System.Text.Encoding]::ASCII.GetBytes($data)
$request.ContentLength = $bytes.Length
$requestStream = [System.IO.Stream]$request.GetRequestStream()
$requestStream.write($bytes, 0, $bytes.Length)
$requestStream.Close()
$response = $request.GetResponse()
$response.GetResponseStream() 

И так как свойство было найдено, то решил попробовать пойти по классике, и получилось это:

[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$false}   
$data = @{"user" = "<USER>";"password" = "<PASSWORD>"} | ConvertTo-JSON
$URi = "https://<URL>"
Invoke-RestMethod -Method Post -Uri $URi -Body $data -ContentType "application/json"