packer-cn/builder/azure/arm/authenticate_cert.go

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package arm
import (
"crypto/ecdsa"
"crypto/rand"
"crypto/rsa"
"crypto/sha1"
"crypto/x509"
"encoding/base64"
"encoding/pem"
"fmt"
"io/ioutil"
"os"
"time"
"github.com/Azure/go-autorest/autorest/azure"
jwt "github.com/dgrijalva/jwt-go"
)
func NewCertOAuthTokenProvider(env azure.Environment, clientID, clientCertPath, tenantID string) (oAuthTokenProvider, error) {
cert, key, err := readCert(clientCertPath)
if err != nil {
return nil, fmt.Errorf("Error reading certificate: %v", err)
}
audience := fmt.Sprintf("%s%s/oauth2/token", env.ActiveDirectoryEndpoint, tenantID)
jwt, err := makeJWT(clientID, audience, cert, key, time.Hour, true)
if err != nil {
return nil, fmt.Errorf("Error generating JWT: %v", err)
}
return NewJWTOAuthTokenProvider(env, clientID, jwt, tenantID), nil
}
// Creates a new JSON Web Token to be used as bearer JWT to authenticate
// to the Azure AD token endpoint to retrieve an access token for `audience`.
// If the full certificate is included in the token, then issuer/subject name
// could be used to authenticate if configured by the identity provider (AAD).
func makeJWT(clientID string, audience string,
cert *x509.Certificate, privatekey interface{},
validFor time.Duration, includeFullCertificate bool) (string, error) {
// The jti (JWT ID) claim provides a unique identifier for the JWT.
// See https://tools.ietf.org/html/rfc7519#section-4.1.7
jti := make([]byte, 20)
_, err := rand.Read(jti)
if err != nil {
return "", err
}
var token *jwt.Token
if cert.PublicKeyAlgorithm == x509.RSA {
token = jwt.New(jwt.SigningMethodRS256)
} else if cert.PublicKeyAlgorithm == x509.ECDSA {
token = jwt.New(jwt.SigningMethodES256)
} else {
return "", fmt.Errorf("Don't know how to handle this type of key algorithm: %v", cert.PublicKeyAlgorithm)
}
hasher := sha1.New()
if _, err := hasher.Write(cert.Raw); err != nil {
return "", err
}
thumbprint := base64.URLEncoding.EncodeToString(hasher.Sum(nil))
// X.509 thumbprint, see https://tools.ietf.org/html/rfc7515#section-4.1.7
token.Header["x5t"] = thumbprint
if includeFullCertificate {
// X.509 certificate (chain), see https://tools.ietf.org/html/rfc7515#section-4.1.6
token.Header["x5c"] = []string{base64.StdEncoding.EncodeToString(cert.Raw)}
}
token.Claims = jwt.MapClaims{
// See https://tools.ietf.org/html/rfc7519#section-4.1
"aud": audience,
"iss": clientID,
"sub": clientID,
"jti": base64.URLEncoding.EncodeToString(jti),
"nbf": time.Now().Unix(),
"exp": time.Now().Add(validFor).Unix(),
}
return token.SignedString(privatekey)
}
func readCert(file string) (cert *x509.Certificate, key interface{}, err error) {
f, err := os.Open(file)
if err != nil {
return nil, nil, err
}
defer f.Close()
d, err := ioutil.ReadAll(f)
if err != nil {
return nil, nil, err
}
blocks := []*pem.Block{}
for len(d) > 0 {
var b *pem.Block
b, d = pem.Decode(d)
if b == nil {
break
}
blocks = append(blocks, b)
}
certs := []*x509.Certificate{}
for _, block := range blocks {
if block.Type == "CERTIFICATE" {
c, err := x509.ParseCertificate(block.Bytes)
if err != nil {
return nil, nil, fmt.Errorf(
"Failed to read certificate block: %v", err)
}
certs = append(certs, c)
} else if block.Type == "PRIVATE KEY" {
key, err = x509.ParsePKCS8PrivateKey(block.Bytes)
if err != nil {
return nil, nil, fmt.Errorf(
"Failed to read private key block: %v", err)
}
}
// Don't care about other types of blocks, ignore
}
if key == nil {
return nil, nil, fmt.Errorf("Did not find private key in pem file")
}
// find the certificate that belongs to the private key by comparing the public keys
switch key := key.(type) {
case *rsa.PrivateKey:
for _, c := range certs {
if cp, ok := c.PublicKey.(*rsa.PublicKey); ok &&
(cp.N.Cmp(key.PublicKey.N) == 0) {
cert = c
}
}
case *ecdsa.PrivateKey:
for _, c := range certs {
if cp, ok := c.PublicKey.(*ecdsa.PublicKey); ok &&
(cp.X.Cmp(key.PublicKey.X) == 0) &&
(cp.Y.Cmp(key.PublicKey.Y) == 0) {
cert = c
}
}
}
if cert == nil {
return nil, nil, fmt.Errorf("Did not find certificate belonging to private key in pem file")
}
return cert, key, nil
}