Visual FoxPro

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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LOCAL lnSuccess
LOCAL loSsh
LOCAL lcHostname
LOCAL lnPort
LOCAL lcXmlResponse
LOCAL loXml
LOCAL lcPassword

lnSuccess = 0

*  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.

loSsh = CreateObject('Chilkat.Ssh')

loSsh.ConnectTimeoutMs = 5000
loSsh.ReadTimeoutMs = 15000

lcHostname = "ssh.example.com"
lnPort = 22
lnSuccess = loSsh.Connect(lcHostname,lnPort)
IF (lnSuccess = 0) THEN
    ? loSsh.LastErrorText
    RELEASE loSsh
    CANCEL
ENDIF

*  Begin keyboard-interactive authentication.  The returned XML describes the server's prompts.
lcXmlResponse = loSsh.StartKeyboardAuth("mySshLogin")
IF (loSsh.LastMethodSuccess = 0) THEN
    ? loSsh.LastErrorText
    RELEASE loSsh
    CANCEL
ENDIF

*  If the server sent a user authentication banner, an application may display it before
*  prompting.
? "UserAuthBanner: " + loSsh.UserAuthBanner

loXml = CreateObject('Chilkat.Xml')
lnSuccess = loXml.LoadXml(lcXmlResponse)
IF (lnSuccess = 0) THEN
    ? loXml.LastErrorText
    RELEASE loSsh
    RELEASE loXml
    CANCEL
ENDIF

*  Authentication is complete when the XML contains either a "success" or an "error" node.
IF (loXml.HasChildWithTag("success")) THEN
    ? "No password required, already authenticated."
    RELEASE loSsh
    RELEASE loXml
    CANCEL
ENDIF

IF (loXml.HasChildWithTag("error")) THEN
    ? "Authentication failed."
    RELEASE loSsh
    RELEASE loXml
    CANCEL
ENDIF

*  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.
lcPassword = "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".
lcXmlResponse = loSsh.ContinueKeyboardAuth(lcPassword)
IF (loSsh.LastMethodSuccess = 0) THEN
    ? loSsh.LastErrorText
    RELEASE loSsh
    RELEASE loXml
    CANCEL
ENDIF

lnSuccess = loXml.LoadXml(lcXmlResponse)
IF (lnSuccess = 0) THEN
    ? loXml.LastErrorText
    RELEASE loSsh
    RELEASE loXml
    CANCEL
ENDIF

IF (loXml.HasChildWithTag("success")) THEN
    ? "SSH keyboard-interactive authentication successful."
    RELEASE loSsh
    RELEASE loXml
    CANCEL
ENDIF

IF (loXml.HasChildWithTag("error")) THEN
    ? "Authentication failed."
ENDIF

RELEASE loSsh
RELEASE loXml