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: sspi.go
    path of file: ./repos/learning/golang/practice/go-crontab/gopath/src/github.com/mongodb/mongo-go-driver/core/auth/internal/gssapi
    
    the code of the file until where you have to start completion: // Copyright (C) MongoDB, Inc. 2017-present.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License. You may obtain
// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0

//+build gssapi,windows
    
func (sc *SaslClient) Start() (string, []byte, error) {
	const mechName = "GSSAPI"

	var cusername *C.char
	var cpassword *C.char
	if sc.username != "" {
		cusername = C.CString(sc.username)
		defer C.free(unsafe.Pointer(cusername))
		if sc.passwordSet {
			cpassword = C.CString(sc.password)
			defer C.free(unsafe.Pointer(cpassword))
		}
	}
	status := C.sspi_client_init(&sc.state, cusername, cpassword)

	if status != C.SSPI_OK {
		return mechName, nil, sc.getError("unable to intitialize client")
	}

	return mechName, nil, nil
}