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token.go
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token.go
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package token
import (
"crypto"
"crypto/x509"
"encoding/base64"
"encoding/json"
"errors"
"fmt"
"strings"
"time"
log "github.com/Sirupsen/logrus"
"github.com/docker/libtrust"
"github.com/docker/distribution/registry/auth"
)
const (
// TokenSeparator is the value which separates the header, claims, and
// signature in the compact serialization of a JSON Web Token.
TokenSeparator = "."
)
// Errors used by token parsing and verification.
var (
ErrMalformedToken = errors.New("malformed token")
ErrInvalidToken = errors.New("invalid token")
)
// ResourceActions stores allowed actions on a named and typed resource.
type ResourceActions struct {
Type string `json:"type"`
Name string `json:"name"`
Actions []string `json:"actions"`
}
// ClaimSet describes the main section of a JSON Web Token.
type ClaimSet struct {
// Public claims
Issuer string `json:"iss"`
Subject string `json:"sub"`
Audience string `json:"aud"`
Expiration int64 `json:"exp"`
NotBefore int64 `json:"nbf"`
IssuedAt int64 `json:"iat"`
JWTID string `json:"jti"`
// Private claims
Access []*ResourceActions `json:"access"`
}
// Header describes the header section of a JSON Web Token.
type Header struct {
Type string `json:"typ"`
SigningAlg string `json:"alg"`
KeyID string `json:"kid,omitempty"`
X5c []string `json:"x5c,omitempty"`
RawJWK json.RawMessage `json:"jwk,omitempty"`
}
// Token describes a JSON Web Token.
type Token struct {
Raw string
Header *Header
Claims *ClaimSet
Signature []byte
}
// VerifyOptions is used to specify
// options when verifying a JSON Web Token.
type VerifyOptions struct {
TrustedIssuers []string
AcceptedAudiences []string
Roots *x509.CertPool
TrustedKeys map[string]libtrust.PublicKey
}
// NewToken parses the given raw token string
// and constructs an unverified JSON Web Token.
func NewToken(rawToken string) (*Token, error) {
parts := strings.Split(rawToken, TokenSeparator)
if len(parts) != 3 {
return nil, ErrMalformedToken
}
var (
rawHeader, rawClaims = parts[0], parts[1]
headerJSON, claimsJSON []byte
err error
)
defer func() {
if err != nil {
log.Errorf("error while unmarshalling raw token: %s", err)
}
}()
if headerJSON, err = joseBase64UrlDecode(rawHeader); err != nil {
err = fmt.Errorf("unable to decode header: %s", err)
return nil, ErrMalformedToken
}
if claimsJSON, err = joseBase64UrlDecode(rawClaims); err != nil {
err = fmt.Errorf("unable to decode claims: %s", err)
return nil, ErrMalformedToken
}
token := new(Token)
token.Header = new(Header)
token.Claims = new(ClaimSet)
token.Raw = strings.Join(parts[:2], TokenSeparator)
if token.Signature, err = joseBase64UrlDecode(parts[2]); err != nil {
err = fmt.Errorf("unable to decode signature: %s", err)
return nil, ErrMalformedToken
}
if err = json.Unmarshal(headerJSON, token.Header); err != nil {
return nil, ErrMalformedToken
}
if err = json.Unmarshal(claimsJSON, token.Claims); err != nil {
return nil, ErrMalformedToken
}
return token, nil
}
// Verify attempts to verify this token using the given options.
// Returns a nil error if the token is valid.
func (t *Token) Verify(verifyOpts VerifyOptions) error {
// Verify that the Issuer claim is a trusted authority.
if !contains(verifyOpts.TrustedIssuers, t.Claims.Issuer) {
log.Errorf("token from untrusted issuer: %q", t.Claims.Issuer)
return ErrInvalidToken
}
// Verify that the Audience claim is allowed.
if !contains(verifyOpts.AcceptedAudiences, t.Claims.Audience) {
log.Errorf("token intended for another audience: %q", t.Claims.Audience)
return ErrInvalidToken
}
// Verify that the token is currently usable and not expired.
currentUnixTime := time.Now().Unix()
if !(t.Claims.NotBefore <= currentUnixTime && currentUnixTime <= t.Claims.Expiration) {
log.Errorf("token not to be used before %d or after %d - currently %d", t.Claims.NotBefore, t.Claims.Expiration, currentUnixTime)
return ErrInvalidToken
}
// Verify the token signature.
if len(t.Signature) == 0 {
log.Error("token has no signature")
return ErrInvalidToken
}
// Verify that the signing key is trusted.
signingKey, err := t.VerifySigningKey(verifyOpts)
if err != nil {
log.Error(err)
return ErrInvalidToken
}
// Finally, verify the signature of the token using the key which signed it.
if err := signingKey.Verify(strings.NewReader(t.Raw), t.Header.SigningAlg, t.Signature); err != nil {
log.Errorf("unable to verify token signature: %s", err)
return ErrInvalidToken
}
return nil
}
// VerifySigningKey attempts to get the key which was used to sign this token.
// The token header should contain either of these 3 fields:
// `x5c` - The x509 certificate chain for the signing key. Needs to be
// verified.
// `jwk` - The JSON Web Key representation of the signing key.
// May contain its own `x5c` field which needs to be verified.
// `kid` - The unique identifier for the key. This library interprets it
// as a libtrust fingerprint. The key itself can be looked up in
// the trustedKeys field of the given verify options.
// Each of these methods are tried in that order of preference until the
// signing key is found or an error is returned.
func (t *Token) VerifySigningKey(verifyOpts VerifyOptions) (signingKey libtrust.PublicKey, err error) {
// First attempt to get an x509 certificate chain from the header.
var (
x5c = t.Header.X5c
rawJWK = t.Header.RawJWK
keyID = t.Header.KeyID
)
switch {
case len(x5c) > 0:
signingKey, err = parseAndVerifyCertChain(x5c, verifyOpts.Roots)
case len(rawJWK) > 0:
signingKey, err = parseAndVerifyRawJWK(rawJWK, verifyOpts)
case len(keyID) > 0:
signingKey = verifyOpts.TrustedKeys[keyID]
if signingKey == nil {
err = fmt.Errorf("token signed by untrusted key with ID: %q", keyID)
}
default:
err = errors.New("unable to get token signing key")
}
return
}
func parseAndVerifyCertChain(x5c []string, roots *x509.CertPool) (leafKey libtrust.PublicKey, err error) {
if len(x5c) == 0 {
return nil, errors.New("empty x509 certificate chain")
}
// Ensure the first element is encoded correctly.
leafCertDer, err := base64.StdEncoding.DecodeString(x5c[0])
if err != nil {
return nil, fmt.Errorf("unable to decode leaf certificate: %s", err)
}
// And that it is a valid x509 certificate.
leafCert, err := x509.ParseCertificate(leafCertDer)
if err != nil {
return nil, fmt.Errorf("unable to parse leaf certificate: %s", err)
}
// The rest of the certificate chain are intermediate certificates.
intermediates := x509.NewCertPool()
for i := 1; i < len(x5c); i++ {
intermediateCertDer, err := base64.StdEncoding.DecodeString(x5c[i])
if err != nil {
return nil, fmt.Errorf("unable to decode intermediate certificate: %s", err)
}
intermediateCert, err := x509.ParseCertificate(intermediateCertDer)
if err != nil {
return nil, fmt.Errorf("unable to parse intermediate certificate: %s", err)
}
intermediates.AddCert(intermediateCert)
}
verifyOpts := x509.VerifyOptions{
Intermediates: intermediates,
Roots: roots,
KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageAny},
}
// TODO: this call returns certificate chains which we ignore for now, but
// we should check them for revocations if we have the ability later.
if _, err = leafCert.Verify(verifyOpts); err != nil {
return nil, fmt.Errorf("unable to verify certificate chain: %s", err)
}
// Get the public key from the leaf certificate.
leafCryptoKey, ok := leafCert.PublicKey.(crypto.PublicKey)
if !ok {
return nil, errors.New("unable to get leaf cert public key value")
}
leafKey, err = libtrust.FromCryptoPublicKey(leafCryptoKey)
if err != nil {
return nil, fmt.Errorf("unable to make libtrust public key from leaf certificate: %s", err)
}
return
}
func parseAndVerifyRawJWK(rawJWK json.RawMessage, verifyOpts VerifyOptions) (pubKey libtrust.PublicKey, err error) {
pubKey, err = libtrust.UnmarshalPublicKeyJWK([]byte(rawJWK))
if err != nil {
return nil, fmt.Errorf("unable to decode raw JWK value: %s", err)
}
// Check to see if the key includes a certificate chain.
x5cVal, ok := pubKey.GetExtendedField("x5c").([]interface{})
if !ok {
// The JWK should be one of the trusted root keys.
if _, trusted := verifyOpts.TrustedKeys[pubKey.KeyID()]; !trusted {
return nil, errors.New("untrusted JWK with no certificate chain")
}
// The JWK is one of the trusted keys.
return
}
// Ensure each item in the chain is of the correct type.
x5c := make([]string, len(x5cVal))
for i, val := range x5cVal {
certString, ok := val.(string)
if !ok || len(certString) == 0 {
return nil, errors.New("malformed certificate chain")
}
x5c[i] = certString
}
// Ensure that the x509 certificate chain can
// be verified up to one of our trusted roots.
leafKey, err := parseAndVerifyCertChain(x5c, verifyOpts.Roots)
if err != nil {
return nil, fmt.Errorf("could not verify JWK certificate chain: %s", err)
}
// Verify that the public key in the leaf cert *is* the signing key.
if pubKey.KeyID() != leafKey.KeyID() {
return nil, errors.New("leaf certificate public key ID does not match JWK key ID")
}
return
}
// accessSet returns a set of actions available for the resource
// actions listed in the `access` section of this token.
func (t *Token) accessSet() accessSet {
if t.Claims == nil {
return nil
}
accessSet := make(accessSet, len(t.Claims.Access))
for _, resourceActions := range t.Claims.Access {
resource := auth.Resource{
Type: resourceActions.Type,
Name: resourceActions.Name,
}
set, exists := accessSet[resource]
if !exists {
set = newActionSet()
accessSet[resource] = set
}
for _, action := range resourceActions.Actions {
set.add(action)
}
}
return accessSet
}
func (t *Token) compactRaw() string {
return fmt.Sprintf("%s.%s", t.Raw, joseBase64UrlEncode(t.Signature))
}