Why can't I authenticate with SshHostKeyFingerprint instead of Password using WinSCP .NET assembly?

Question

This script is an example from here: https://winscp.net/eng/docs/library_powershell

I have just edited paths and session options.

I can successfully connect with to the sftp server with the private key in WinSCP GUI.

try
{
    # Load WinSCP .NET assembly
    Add-Type -Path "C:\Program Files (x86)\WinSCP\WinSCPnet.dll"

    # Setup session options
    $sessionOptions = New-Object WinSCP.SessionOptions -Property @{
        Protocol = [WinSCP.Protocol]::Sftp
        HostName = "test.sftp.com"
        UserName = "customer_TEST"
        # I do not want to use this: Password = "mypassword"
        SshHostKeyFingerprint = "ssh-rsa 2048 SHA256:*********"
    }

    $session = New-Object WinSCP.Session

    try
    {
        # Connect
        $session.Open($sessionOptions)

        # Upload files
        $transferOptions = New-Object WinSCP.TransferOptions
        $transferOptions.TransferMode = [WinSCP.TransferMode]::Binary

        $transferResult =
        $session.PutFiles("D:\test\*", "/home/user/", $False, $transferOptions)

        # Throw on any error
        $transferResult.Check()

        # Print results
        foreach ($transfer in $transferResult.Transfers)
        {
            Write-Host "Upload of $($transfer.FileName) succeeded"
        }
    }
    finally
    {
        # Disconnect, clean up
        $session.Dispose()
    }
    exit 0
}
catch
{
    Write-Host "Error: $($_.Exception.Message)"
    exit 1
}

Answer 1

SSH host key fingerprint is not an authentication method. It's a way to verify an identity of the server, not yours. See Understanding SSH key pairs.

If you want to use public key authentication, you need to set SessionOptions.SshPrivateKeyPath (or SessionOptions.SshPrivateKey).

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And you will have to set SshHostKeyFingerprint correctly, as your current value will throw an error:
WinSCP .NET assembly in PowerShell - Creating SessionOptions - The value supplied is not valid, or the property is read-only