Ruby

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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Ruby

require 'chilkat'

success = 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.

ssh = Chilkat::CkSsh.new()

ssh.put_ConnectTimeoutMs(5000)
ssh.put_ReadTimeoutMs(15000)

hostname = "ssh.example.com"
port = 22
success = ssh.Connect(hostname,port)
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

#  Begin keyboard-interactive authentication.  The returned XML describes the server's prompts.
xmlResponse = ssh.startKeyboardAuth("mySshLogin")
if (ssh.get_LastMethodSuccess() == false)
    print ssh.lastErrorText() + "\n";
    exit
end

#  If the server sent a user authentication banner, an application may display it before
#  prompting.
print "UserAuthBanner: " + ssh.userAuthBanner() + "\n";

xml = Chilkat::CkXml.new()
success = xml.LoadXml(xmlResponse)
if (success == false)
    print xml.lastErrorText() + "\n";
    exit
end

#  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
end

if (xml.HasChildWithTag("error"))
    print "Authentication failed." + "\n";
    exit
end

#  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.
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.get_LastMethodSuccess() == false)
    print ssh.lastErrorText() + "\n";
    exit
end

success = xml.LoadXml(xmlResponse)
if (success == false)
    print xml.lastErrorText() + "\n";
    exit
end

if (xml.HasChildWithTag("success"))
    print "SSH keyboard-interactive authentication successful." + "\n";
    exit
end

if (xml.HasChildWithTag("error"))
    print "Authentication failed." + "\n";
end