VB.NET

SSH Keyboard-Interactive Authentication

Demonstrates keyboard-interactive authentication with an SSH server. StartKeyboardAuth returns XML describing the server's prompts, and ContinueKeyboardAuth submits each response. Authentication is complete when the returned XML contains either a success or an error node.

Background: Keyboard-interactive is SSH's flexible, prompt-driven method: rather than assuming a single password, the server asks one or more questions — a password, a one-time code, a security question — and the client answers each. This is how SSH supports two-factor and other challenge-response schemes. The prompt XML also indicates whether each response should be echoed, so a client knows when to mask input. A server may issue several rounds, so a robust implementation loops until it sees success or error rather than assuming one exchange is enough.

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VB.NET

Dim success As Boolean = False

'  This example requires the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

'  Demonstrates keyboard-interactive authentication with an SSH server.  The server sends one or
'  more prompts as XML, and the application answers each with ContinueKeyboardAuth.

Dim ssh As New Chilkat.Ssh

ssh.ConnectTimeoutMs = 5000
ssh.ReadTimeoutMs = 15000

Dim hostname As String = "ssh.example.com"
Dim port As Integer = 22
success = ssh.Connect(hostname,port)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  Begin keyboard-interactive authentication.  The returned XML describes the server's prompts.
Dim xmlResponse As String = ssh.StartKeyboardAuth("mySshLogin")
If (ssh.LastMethodSuccess = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  If the server sent a user authentication banner, an application may display it before
'  prompting.
Debug.WriteLine("UserAuthBanner: " & ssh.UserAuthBanner)

Dim xml As New Chilkat.Xml
success = xml.LoadXml(xmlResponse)
If (success = False) Then
    Debug.WriteLine(xml.LastErrorText)
    Exit Sub
End If


'  Authentication is complete when the XML contains either a "success" or an "error" node.
If (xml.HasChildWithTag("success")) Then
    Debug.WriteLine("No password required, already authenticated.")
    Exit Sub
End If


If (xml.HasChildWithTag("error")) Then
    Debug.WriteLine("Authentication failed.")
    Exit Sub
End If


'  Normally you would not hard-code the password in source.  You should instead obtain it
'  from an interactive prompt, environment variable, or a secrets vault.
Dim password As String = "mySshPassword"

'  Answer the prompt.  Typically one call is enough, but a server may issue several rounds of
'  prompts, so a robust client loops until it sees "success" or "error".
xmlResponse = ssh.ContinueKeyboardAuth(password)
If (ssh.LastMethodSuccess = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


success = xml.LoadXml(xmlResponse)
If (success = False) Then
    Debug.WriteLine(xml.LastErrorText)
    Exit Sub
End If


If (xml.HasChildWithTag("success")) Then
    Debug.WriteLine("SSH keyboard-interactive authentication successful.")
    Exit Sub
End If


If (xml.HasChildWithTag("error")) Then
    Debug.WriteLine("Authentication failed.")
End If