Perl

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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use strict;
use warnings;
use Chilkat2;

# 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.

my $ssh = Chilkat2::Ssh->new;

$ssh->ConnectTimeoutMs(5000);
$ssh->ReadTimeoutMs(15000);

my $hostname = 'ssh.example.com';
my $port = 22;
my $success = $ssh->Connect($hostname, $port);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# Begin keyboard-interactive authentication.  The returned XML describes the server's prompts.
my $xmlResponse = $ssh->StartKeyboardAuth('mySshLogin');
if (!$ssh->LastMethodSuccess) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# If the server sent a user authentication banner, an application may display it before
# prompting.
print 'UserAuthBanner: ', $ssh->UserAuthBanner, "\n";

my $xml = Chilkat2::Xml->new;
$success = $xml->LoadXml($xmlResponse);
if (!$success) {
    print $xml->LastErrorText, "\n";
    exit;
}

# Authentication is complete when the XML contains either a "success" or an "error" node.
if ($xml->HasChildWithTag('success')) {
    print "No password required, already authenticated.\n";
    exit;
}

if ($xml->HasChildWithTag('error')) {
    print "Authentication failed.\n";
    exit;
}

# 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.
my $password = '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) {
    print $ssh->LastErrorText, "\n";
    exit;
}

$success = $xml->LoadXml($xmlResponse);
if (!$success) {
    print $xml->LastErrorText, "\n";
    exit;
}

if ($xml->HasChildWithTag('success')) {
    print "SSH keyboard-interactive authentication successful.\n";
    exit;
}

if ($xml->HasChildWithTag('error')) {
    print "Authentication failed.\n";
}