How to suppress "keyboard-interactive" prompts in plink.exe - powershell

Question

I have a PowerShell script that calls plink.exe regularly. Normally, the two output lines about keyboard-interactive prompts are simply annoying.
However, when run using Start-Job, they get output as error text as soon as I call Receive-Job.
Is there any way to suppress these? I'd rather not suppress all errors.
My test code:
$test_scriptblock = [scriptblock]::Create(#"
param(
`$argumentlist
)
`$pw = `$argumentlist.pw
& 'C:\Program Files\Putty\Plink.exe' -ssh `"admin#*.*.*.*" -pw `$pw -batch whoami
"#)
$testParm = #{
pw = Read-Host "password"
}
$testjob = Start-Job -scriptblock $test_scriptblock -Argumentlist $testParm
$i = 0
do {
$i++
sleep 2
$results = Receive-Job $testjob
ForEach ($result in $results) {
Write-Host $result
}
if ($testjob.State -eq "Completed") {
$jobcompleted = $true
}
If ($i -gt 10) {
Stop-job $testjob
$jobcompleted = $true
}
} until ($jobcompleted)

Answer 1

Just add the stderr redirect to your plink or pscp commandline, to an extra dummy file, like
pscp ... 2> stderr.txt
With a caveat that it may swallow other valid error msgs, at your own risk :)

Answer 2

There's no way to suppress keyboard-interactive prompts in Plink.
I suggest you use a native .NET SSH implementation, like SSH.NET instead of driving an external console application.

Answer 3

Ir was a bit cumbersome, but finally I managed to suppress the "keyboard-interactive" messages this way:
[String] $Plink = 'C:\Program Files\PuTTY\plink.exe'
[Array] $PlinkPar = #("-ssh", "-l", $usr, "-pw", $pwd, $hst) # Set plink parameters
[Boolean] $PlinkOK = $True
Write-Host "Accept possibly unknown host key"
"y" | & $Plink $PlinkPar "exit" 2>&1 | Tee-Object -Variable PlinkOut | Out-Null
$PlinkOut | Foreach-Object {
$PlinkStr = $_.ToString()
If ($_ -is [System.Management.Automation.ErrorRecord]) {
If (! $PlinkStr.Contains("eyboard-interactive")) {
Write-Host "Error: $PlinkStr"
$PlinkOK = $False
}
} else {
Write-Host "$PlinkStr"
}
}
If (! $PlinkOK) { exit }
$PlinkPar += "-batch
And the output is like this:
>powershell .\InstCR.ps1 -usr myuser -pwd mypassword -hst doesnotexist
Accept possibly unknown host key
Error: Unable to open connection:
Error: Host does not exist
This plink call is just to accept a possibly unknown host key (without "-batch" and piping the "y" to answer the prompt). Then "-batch" is added to the Plink parameters to be used on all subsequent plink calls.