You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: client_auth.go
    path of file: ./repos/awless/vendor/golang.org/x/crypto/ssh
    
    the code of the file until where you have to start completion: // Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package ssh

import (
	"bytes"
	"errors"
	"fmt"
	"io"
)

// clientAuthenticate authenticates with the remote server. See RFC 4252.
func (c *connection) clientAuthenticate(config *ClientConfig) error {
	// initiate user auth session
	if err := c.transport.writePacket(Marshal(&serviceRequestMsg{serviceUserAuth})); err != nil {
		return err
	}
	packet, err := c.transport.readPacket()
	if err != nil {
		return err
	}
	var serviceAccept serviceAcceptMsg
	if err := Unmarshal(packet, &serviceAccept); err != nil {
		return err
	}

	// during the authentication phase the client first attempts the "none" method
	// then any untried methods suggested by the server.
	tried := make(map[string]bool)
	var lastMethods []string

	sessionID := c.transport.getSessionID()
	for auth := AuthMethod(new(noneAuth)); auth != nil; {
		ok, methods, err := auth.auth(sessionID, config.User, c.transport, config.Rand)
		if err != nil {
			return err
		}
		if ok {
			// success
			return nil
		}
		tried[auth.method()] = true
		if methods == nil {
			methods = lastMethods
		}
		lastMethods = methods

		auth = nil

	findNext:
		for _, a := range config.Auth {
			candidateMetho
    
func (cb KeyboardInteractiveChallenge) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
	type initiateMsg struct {
		User       string `sshtype:"50"`
		Service    string
		Method     string
		Language   string
		Submethods string
	}

	if err := c.writePacket(Marshal(&initiateMsg{
		User:    user,
		Service: serviceSSH,
		Method:  "keyboard-interactive",
	})); err != nil {
		return false, nil, err
	}

	for {
		packet, err := c.readPacket()
		if err != nil {
			return false, nil, err
		}

		// like handleAuthResponse, but with less options.
		switch packet[0] {
		case msgUserAuthBanner:
			if err := handleBannerResponse(c, packet); err != nil {
				return false, nil, err
			}
			continue
		case msgUserAuthInfoRequest:
			// OK
		case msgUserAuthFailure:
			var msg userAuthFailureMsg
			if err := Unmarshal(packet, &msg); err != nil {
				return false, nil, err
			}
			return false, msg.Methods, nil
		case msgUserAuthSuccess:
			return true, nil, nil
		default:
			return false, nil, unexpectedMessageError(msgUserAuthInfoRequest, packet[0])
		}

		var msg userAuthInfoRequestMsg
		if err := Unmarshal(packet, &msg); err != nil {
			return false, nil, err
		}

		// Manually unpack the prompt/echo pairs.
		rest := msg.Prompts
		var prompts []string
		var echos []bool
		for i := 0; i < int(msg.NumPrompts); i++ {
			prompt, r, ok := parseString(rest)
			if !ok || len(r) == 0 {
				return false, nil, errors.New("ssh: prompt format error")
			}
			prompts = append(prompts, string(prompt))
			echos = append(echos, r[0] != 0)
			rest = r[1:]
		}

		if len(rest) != 0 {
			return false, nil, errors.New("ssh: extra data following keyboard-interactive pairs")
		}

		answers, err := cb(msg.User, msg.Instruction, prompts, echos)
		if err != nil {
			return false, nil, err
		}

		if len(answers) != len(prompts) {
			return false, nil, errors.New("ssh: not enough answers from keyboard-interactive callback")
		}
		responseLength := 1 + 4
		for _, a := range answers {
			responseLength += stringLength(len(a))
		}
		serialized := make([]byte, responseLength)
		p := serialized
		p[0] = msgUserAuthInfoResponse
		p = p[1:]
		p = marshalUint32(p, uint32(len(answers)))
		for _, a := range answers {
			p = marshalString(p, []byte(a))
		}

		if err := c.writePacket(serialized); err != nil {
			return false, nil, err
		}
	}
}