Windows OpenSSH (ssh.exe) with a password, non-interactively, from PowerShell: SSH_ASKPASS + SSH_ASKPASS_REQUIRE=force

Write a tiny askpass helper that prints only the password, point SSH_ASKPASS at it, and force its use:

$askDir = Join-Path ([IO.Path]::GetTempPath()) ('ssh_' + [Guid]::NewGuid().ToString('N'))
New-Item -ItemType Directory -Path $askDir -Force | Out-Null
$askPath = Join-Path $askDir 'askpass.cmd'
Set-Content -Path $askPath -Value "@echo off`r`necho $pass" -Encoding Ascii
try {
  $psi = New-Object Diagnostics.ProcessStartInfo
  $psi.FileName = 'ssh.exe'
  $psi.Arguments = "-o BatchMode=no -o StrictHostKeyChecking=accept-new -o NumberOfPasswordPrompts=1 " +
                   "-o PreferredAuthentications=password -o ConnectTimeout=8 -p 22 $user@$ip `"$remoteCmd`""
  $psi.UseShellExecute = $false; $psi.RedirectStandardOutput = $true; $psi.RedirectStandardError = $true
  $psi.EnvironmentVariables['SSH_ASKPASS'] = $askPath
  $psi.EnvironmentVariables['SSH_ASKPASS_REQUIRE'] = 'force'
  if (-not $psi.EnvironmentVariables.ContainsKey('DISPLAY')) { $psi.EnvironmentVariables['DISPLAY'] = 'localhost:0' }
  $p = [Diagnostics.Process]::Start($psi)
  $out = $p.StandardOutput.ReadToEnd(); $null = $p.StandardError.ReadToEnd()
  if (-not $p.WaitForExit(13000)) { $p.Kill() }
} finally { Remove-Item -Recurse -Force $askDir -ErrorAction SilentlyContinue }

Notes:

• Build a single Arguments string; ArgumentList does not exist on .NET Framework before 4.7.2.
• To read binary data, have the remote side encode it: dd if=FILE bs=1 skip=N count=M 2>/dev/null | base64 | tr -d '\n'.
• Same code on macOS/Linux for testing: write an askpass.sh and chmod +x it. Detect the platform with Test-Path 'variable:IsWindows': $IsWindows does not exist in Windows PowerShell 5.1, and under Set-StrictMode a bare reference throws VariableIsUndefined.