Add util to create bearer JWTs

builder/azure/cmd/mkbearerjwt/main.go

@@ -0,0 +1,159 @@
+package main
+
+import (
+	"crypto/ecdsa"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha1"
+	"crypto/x509"
+	"encoding/base64"
+	"encoding/pem"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"time"
+
+	jwt "github.com/dgrijalva/jwt-go"
+)
+
+func main() {
+	var (
+		certfile string
+		duration time.Duration
+		addX5c   bool
+		audience string
+		clientID string
+	)
+	flag.StringVar(&clientID, "clientId", "", "The ID of the client that is going to use this token (sub)")
+	flag.DurationVar(&duration, "validFor", time.Hour, "Validity duration")
+	flag.StringVar(&audience, "audience", "", "Target audience, usually \"https://login.microsoftonline.com/<tenantid>/oauth2/token\"")
+	flag.StringVar(&certfile, "cert", "", "Certificate file")
+	flag.BoolVar(&addX5c, "x5c", false, "Add x5c header with full certificate (needed for issuer/subject name authentication)")
+	flag.Parse()
+	if certfile == "" || audience == "" || clientID == "" {
+		fmt.Println("Create a bearer JWT for client authentication from a certificate")
+		flag.PrintDefaults()
+		os.Exit(-1)
+	}
+
+	cert, key, err := readCert(certfile)
+	if err != nil {
+		fmt.Println("Error reading certificate:", err)
+		os.Exit(-1)
+	}
+
+	jwt, err := makeJWT(clientID, audience, cert, key, duration, addX5c)
+	if err != nil {
+		fmt.Println("Error generating JWT:", err)
+		os.Exit(-1)
+	}
+	fmt.Println(jwt)
+}
+
+func makeJWT(clientID string, audience string, cert *x509.Certificate, privatekey interface{}, validFor time.Duration, includeX5c bool) (string, error) {
+	// The jti (JWT ID) claim provides a unique identifier for the JWT.
+	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
+	}
+	token.Header["x5t"] = base64.URLEncoding.EncodeToString(hasher.Sum(nil))
+	if includeX5c {
+		token.Header["x5c"] = []string{base64.StdEncoding.EncodeToString(cert.Raw)}
+	}
+
+	token.Claims = jwt.MapClaims{
+		"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)
+			}
+		}
+	}
+
+	if key == nil {
+		return nil, nil, fmt.Errorf("Did not find private key in pem file")
+	}
+
+	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
+}