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certificate.go
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certificate.go
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/*
Copyright 2020 Banzai Cloud.
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 cert
import (
"crypto/tls"
"crypto/x509"
"encoding/pem"
"io/ioutil"
"os"
"path"
"time"
)
const (
// CAKeyName is the name of the CA private key
CAKeyName = "ca.key"
// CACertName is the name of the CA certificate
CACertName = "ca.crt"
// ServerKeyName is the name of the server private key
ServerKeyName = "tls.key"
// ServerCertName is the name of the serving certificate
ServerCertName = "tls.crt"
)
type Certificate struct {
// PEM encoded private key
Key []byte
// PEM encoded serving certificate
Cert []byte
// PEM encoded CA private key
CAKey []byte
// PEM encoded CA certificate
CACert []byte
}
func ReadCertificate(dir string) (*Certificate, error) {
return (&Certificate{}).Read(dir)
}
func (cert *Certificate) Read(dir string) (*Certificate, error) {
filenames := []string{CAKeyName, CACertName, ServerCertName, ServerKeyName}
for _, filename := range filenames {
if !fileExists(path.Join(dir, filename)) {
continue
}
content, err := ioutil.ReadFile(path.Join(dir, filename))
if err != nil {
return nil, err
}
switch filename {
case CAKeyName:
cert.CAKey = content
case CACertName:
cert.CACert = content
case ServerCertName:
cert.Cert = content
case ServerKeyName:
cert.Key = content
}
}
return cert, nil
}
func (cert Certificate) Write(dir string) error {
err := os.MkdirAll(dir, 0755)
if err != nil {
return err
}
for file, content := range map[string][]byte{
CAKeyName: cert.CAKey,
CACertName: cert.CACert,
ServerCertName: cert.Cert,
ServerKeyName: cert.Key,
} {
err = writeFile(dir+"/"+file, content)
if err != nil {
return err
}
}
return nil
}
func (cert *Certificate) Verify(dnsName string, checkTime time.Time) bool {
if cert == nil || cert.Key == nil || cert.Cert == nil {
return false
}
// Verify key and cert are valid pair
_, err := tls.X509KeyPair(cert.Cert, cert.Key)
if err != nil {
return false
}
// Verify cert is good for desired DNS name and signed by CA and will be valid for desired period of time.
pool := x509.NewCertPool()
if !pool.AppendCertsFromPEM(cert.CACert) {
return false
}
block, _ := pem.Decode([]byte(cert.Cert))
if block == nil {
return false
}
certificate, err := x509.ParseCertificate(block.Bytes)
if err != nil {
return false
}
ops := x509.VerifyOptions{
DNSName: dnsName,
Roots: pool,
CurrentTime: checkTime,
}
_, err = certificate.Verify(ops)
return err == nil
}
func fileExists(filename string) bool {
info, err := os.Stat(filename)
if os.IsNotExist(err) {
return false
}
return !info.IsDir()
}
func writeFile(filepath string, content []byte) error {
f, err := os.Create(filepath)
if err != nil {
return err
}
defer f.Close()
_, err = f.Write(content)
if err != nil {
return err
}
return nil
}