/
generate_jwt.go
196 lines (173 loc) · 5.06 KB
/
generate_jwt.go
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// Copyright 2023 Aalyria Technologies, Inc., and its affiliates.
//
// 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 main provides a simple utility to generate signed JWTs.
package main
import (
"bytes"
"context"
"crypto"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/json"
"encoding/pem"
"errors"
"flag"
"fmt"
"io"
"os"
"time"
)
func main() {
if err := run(context.Background()); err != nil {
fmt.Fprintf(os.Stderr, "fatal error: %s\n", err)
os.Exit(2)
}
}
func run(ctx context.Context) error {
fs := flag.NewFlagSet("generate_jwt", flag.ContinueOnError)
var (
lifetime = fs.Duration("lifetime", 1*time.Hour, "Lifetime that the JWT will be valid for")
audience = fs.String("audience", "", "Audience (aud) for the JWT")
issuer = fs.String("issuer", "", "Issuer (iss) for the JWT")
subject = fs.String("subject", "", "Subject (sub) for the JWT; defaults to the issuer")
targetAudience = fs.String("target-audience", "", "JWT 'target_audience' field")
keyID = fs.String("key-id", "", "The ID corresponding to the private key")
privKeyPath = fs.String("private-key", "", "Path to the RSA private key file in either PKCS8 or PKCS1, ASN.1 DER form (PEM-encoded) used to sign the JWT")
)
if err := fs.Parse(os.Args[1:]); err != nil {
return err
}
if *audience == "" {
return errors.New("no audience provided")
}
if *issuer == "" {
return errors.New("no issuer provided")
}
if *keyID == "" {
return errors.New("no key-id provided")
}
if *subject == "" {
subject = issuer
}
jwt, err := generateJWT(*issuer, *subject, *audience, *targetAudience, *keyID, *privKeyPath, *lifetime)
if err != nil {
return err
}
fmt.Println(string(jwt))
return nil
}
func generateJWT(issuer, subject, audience, targetAudience, keyID, keyPath string, lifetime time.Duration) ([]byte, error) {
privKey, err := decodePrivateKey(keyPath)
if err != nil {
return nil, err
}
headerBytes, err := generateHeader(keyID)
if err != nil {
return nil, err
}
payloadBytes, err := generatePayload(issuer, subject, audience, targetAudience, lifetime)
if err != nil {
return nil, err
}
sigBytes, err := generateSignature(headerBytes, payloadBytes, privKey)
if err != nil {
return nil, err
}
return bytes.Join([][]byte{headerBytes, payloadBytes, sigBytes}, []byte(".")), nil
}
func generateHeader(keyID string) ([]byte, error) {
return base64EncodeJSON(map[string]interface{}{
"alg": "RS256",
"typ": "JWT",
"kid": keyID,
})
}
func generatePayload(issuer, subject, audience, targetAudience string, lifetime time.Duration) ([]byte, error) {
now := time.Now()
payload := map[string]interface{}{
"aud": audience,
"exp": now.Add(lifetime).Unix(),
"iat": now.Unix(),
"iss": issuer,
"sub": subject,
}
if targetAudience != "" {
payload["target_audience"] = targetAudience
}
return base64EncodeJSON(payload)
}
func generateSignature(headerBytes, payloadBytes []byte, privKey *rsa.PrivateKey) ([]byte, error) {
hasher := sha256.New()
hasher.Write(headerBytes)
hasher.Write([]byte("."))
hasher.Write(payloadBytes)
rawSig, err := rsa.SignPKCS1v15(rand.Reader, privKey, crypto.SHA256, hasher.Sum(nil))
if err != nil {
return nil, err
}
return base64Encode(rawSig)
}
func decodePrivateKey(keyPath string) (*rsa.PrivateKey, error) {
f, err := os.Open(keyPath)
if err != nil {
return nil, err
}
defer f.Close()
keyBytes, err := io.ReadAll(f)
if err != nil {
return nil, err
}
block, _ := pem.Decode(keyBytes)
return parsePrivateKey(block.Bytes)
}
func parsePrivateKey(data []byte) (*rsa.PrivateKey, error) {
errs := []error{}
pkcs8Key, err := x509.ParsePKCS8PrivateKey(data)
if err == nil {
if rsaPrivKey, ok := pkcs8Key.(*rsa.PrivateKey); ok {
return rsaPrivKey, nil
}
errs = append(errs, fmt.Errorf("unexpected pkcs8 key type: %v", pkcs8Key))
} else {
errs = append(errs, fmt.Errorf("error parsing key as pkcs8: %w", err))
}
pkcs1Key, err := x509.ParsePKCS1PrivateKey(data)
if err == nil {
return pkcs1Key, nil
} else {
errs = append(errs, fmt.Errorf("error parsing key as pkcs1: %w", err))
}
return nil, errors.Join(errs...)
}
func base64EncodeJSON(inp map[string]interface{}) ([]byte, error) {
data, err := json.Marshal(inp)
if err != nil {
return nil, err
}
return base64Encode(data)
}
func base64Encode(data []byte) ([]byte, error) {
buf := bytes.Buffer{}
enc := base64.NewEncoder(base64.RawURLEncoding, &buf)
if _, err := enc.Write(data); err != nil {
return nil, err
}
if err := enc.Close(); err != nil {
return nil, err
}
return buf.Bytes(), nil
}