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: kerberos.go
    path of file: ./repos/franz-go/pkg/sasl/kerberos
    
    the code of the file until where you have to start completion: // Package kerberos provides Kerberos v5 sasl authentication.
package kerberos

import (
	"context"
	"encoding/binary"
	"fmt"
	"net"
	"runtime"
	"st
    
func (s *session) Challenge(resp []byte) (bool, []byte, error) {
	step := s.step
	s.step++
	switch step {
	case 0:
		var challenge gssapi.WrapToken
		if err := challenge.Unmarshal(resp, true); err != nil {
			return false, nil, err
		}
		isValid, err := challenge.Verify(s.encKey, 22) // 22 == GSSAPI ACCEPTOR SEAL
		if !isValid {
			return false, nil, err
		}
		response, err := gssapi.NewInitiatorWrapToken(challenge.Payload, s.encKey)
		if err != nil {
			return false, nil, err
		}
		marshalled, err := response.Marshal()
		return true, marshalled, err // we are done, but we have one more response to write ourselves
	default:
		return false, nil, fmt.Errorf("challenge / response should be done, but still going at %d", step)
	}
}