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: tls.go
    path of file: ./repos/jackal/pkg/util/tls
    
    the code of the file until where you have to start completion: // Copyright 2022 The jackal Authors
//
// 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
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package tlsutil

import (
	"crypto/rand"
	"crypto/rsa"
	
    
func LoadCertificate(keyFile, certFile, domain string) (tls.Certificate, error) {
	if len(certFile) == 0 || len(keyFile) == 0 {
		switch domain {
		case localhostDomain:
			if !selfSignedCertificateExists() {
				err := generateSelfSignedCertificate(selfSignedCertPrivateKey, selfSignedCertFile, domain)
				if err != nil {
					return tls.Certificate{}, err
				}
			}
			keyFile = selfSignedCertPrivateKey
			certFile = selfSignedCertFile

		default:
			return tls.Certificate{}, fmt.Errorf("must specify a private key and a server certificate for the domain '%s'", domain)
		}
	}
	cer, err := tls.LoadX509KeyPair(certFile, keyFile)
	if err != nil {
		return tls.Certificate{}, err
	}
	return cer, nil
}