internal/tls/tls.go

/*
Copyright 2025 The Kubernetes 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 tls

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"math/big"
	"time"

	"github.com/go-logr/logr"
)

// CreateSelfSignedTLSCertificate creates a self-signed cert the server can use to serve TLS.
func CreateSelfSignedTLSCertificate(logger logr.Logger) (tls.Certificate, error) {
	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("error creating serial number: %v", err)
	}
	now := time.Now()
	notBefore := now.UTC()
	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{"Inference Ext"},
		},
		NotBefore:             notBefore,
		NotAfter:              now.Add(time.Hour * 24 * 365 * 10).UTC(), // 10 years
		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	priv, err := rsa.GenerateKey(rand.Reader, 4096)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("error generating key: %v", err)
	}

	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("error creating certificate: %v", err)
	}

	certBytes := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes})

	privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("error marshalling private key: %v", err)
	}
	keyBytes := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: privBytes})

	return tls.X509KeyPair(certBytes, keyBytes)
}