From: terrafrost <terrafrost@gmail.com>
Date: Sun, 2 May 2021 08:15:00 -0500
Subject: Support for continue auth methods.

Origin: upstream, https://github.com/phpseclib/phpseclib/commit/f1b0708446a5ae9f206c626efcf42680562bc5ee
---
 phpseclib/Net/SSH2.php | 35 +++++++++++++++++++++++++++++++----
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index 7bd5635..35dd0ca 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -970,6 +970,14 @@ class SSH2
      */
     var $auth = array();
 
+    /**
+     * The authentication methods that may productively continue authentication.
+     * 
+     * @see https://tools.ietf.org/html/rfc4252#section-5.1
+     * @var array|null 
+     */
+    private $auth_methods_to_continue = null;
+
     /**
      * Default Constructor.
      *
@@ -2131,7 +2139,7 @@ class SSH2
 
         // try logging with 'none' as an authentication method first since that's what
         // PuTTY does
-        if (substr($this->server_identifier, 0, 13) != 'SSH-2.0-CoreFTP') {
+        if (substr($this->server_identifier, 0, 13) != 'SSH-2.0-CoreFTP' && $this->auth_methods_to_continue === null) {
             if ($this->_login($username)) {
                 return true;
             }
@@ -2275,7 +2283,9 @@ class SSH2
                 case NET_SSH2_MSG_USERAUTH_SUCCESS:
                     $this->bitmap |= self::MASK_LOGIN;
                     return true;
-                //case NET_SSH2_MSG_USERAUTH_FAILURE:
+                case NET_SSH2_MSG_USERAUTH_FAILURE:
+                    extract(unpack('Nmethodlistlen', $this->_string_shift($response, 4)));
+                    $this->auth_methods_to_continue = explode(',', $this->_string_shift($response, $methodlistlen));
                 default:
                     return false;
             }
@@ -2347,6 +2357,7 @@ class SSH2
                 }
                 extract(unpack('Nlength', $this->_string_shift($response, 4)));
                 $auth_methods = explode(',', $this->_string_shift($response, $length));
+                $this->auth_methods_to_continue = $auth_methods;
                 if (!strlen($response)) {
                     return false;
                 }
@@ -2519,6 +2530,8 @@ class SSH2
             case NET_SSH2_MSG_USERAUTH_SUCCESS:
                 return true;
             case NET_SSH2_MSG_USERAUTH_FAILURE:
+                extract(unpack('Nmethodlistlen', $this->_string_shift($response, 4)));
+                $this->auth_methods_to_continue = explode(',', $this->_string_shift($response, $methodlistlen));
                 return false;
         }
 
@@ -2627,8 +2640,9 @@ class SSH2
                 if (strlen($response) < 4) {
                     return false;
                 }
-                extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                $this->errors[] = 'SSH_MSG_USERAUTH_FAILURE: ' . $this->_string_shift($response, $length);
+                extract(unpack('Nmethodlistlen', $this->_string_shift($response, 4)));
+                $this->auth_methods_to_continue = explode(',', $this->_string_shift($response, $methodlistlen));
+                $this->errors[] = 'SSH_MSG_USERAUTH_FAILURE';
                 return false;
             case NET_SSH2_MSG_USERAUTH_PK_OK:
                 // we'll just take it on faith that the public key blob and the public key algorithm name are as
@@ -2662,6 +2676,8 @@ class SSH2
         switch ($type) {
             case NET_SSH2_MSG_USERAUTH_FAILURE:
                 // either the login is bad or the server employs multi-factor authentication
+                extract(unpack('Nmethodlistlen', $this->_string_shift($response, 4)));
+                $this->auth_methods_to_continue = explode(',', $this->_string_shift($response, $methodlistlen));
                 return false;
             case NET_SSH2_MSG_USERAUTH_SUCCESS:
                 $this->bitmap |= self::MASK_LOGIN;
@@ -5150,4 +5166,15 @@ class SSH2
             );
         }
     }
+
+    /**
+     * Return the list of authentication methods that may productively continue authentication.
+     * 
+     * @see https://tools.ietf.org/html/rfc4252#section-5.1
+     * @return array|null
+     */
+    public function getAuthMethodsToContinue()
+    {
+        return $this->auth_methods_to_continue;
+    }
 }