C++

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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C++

#include <CkSsh.h>
#include <CkXml.h>

void ChilkatSample(void)
    {
    bool 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.

    CkSsh ssh;

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

    const char *hostname = "ssh.example.com";
    int port = 22;
    success = ssh.Connect(hostname,port);
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    //  Begin keyboard-interactive authentication.  The returned XML describes the server's prompts.
    const char *xmlResponse = ssh.startKeyboardAuth("mySshLogin");
    if (ssh.get_LastMethodSuccess() == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    //  If the server sent a user authentication banner, an application may display it before
    //  prompting.
    std::cout << "UserAuthBanner: " << ssh.userAuthBanner() << "\r\n";

    CkXml xml;
    success = xml.LoadXml(xmlResponse);
    if (success == false) {
        std::cout << xml.lastErrorText() << "\r\n";
        return;
    }

    //  Authentication is complete when the XML contains either a "success" or an "error" node.
    if (xml.HasChildWithTag("success")) {
        std::cout << "No password required, already authenticated." << "\r\n";
        return;
    }

    if (xml.HasChildWithTag("error")) {
        std::cout << "Authentication failed." << "\r\n";
        return;
    }

    //  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.
    const char *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) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    success = xml.LoadXml(xmlResponse);
    if (success == false) {
        std::cout << xml.lastErrorText() << "\r\n";
        return;
    }

    if (xml.HasChildWithTag("success")) {
        std::cout << "SSH keyboard-interactive authentication successful." << "\r\n";
        return;
    }

    if (xml.HasChildWithTag("error")) {
        std::cout << "Authentication failed." << "\r\n";
    }
    }