token/hmac: Add ability to rotate HMAC keys

compose/compose.go

@@ -95,7 +95,7 @@ func ComposeAllEnabled(config *Config, storage interface{}, secret []byte, key *
 		config,
 		storage,
 		&CommonStrategy{
-			CoreStrategy:               NewOAuth2HMACStrategy(config, secret),
+			CoreStrategy:               NewOAuth2HMACStrategy(config, secret, nil),
 			OpenIDConnectTokenStrategy: NewOpenIDConnectStrategy(config, key),
 			JWTStrategy: &jwt.RS256JWTStrategy{
 				PrivateKey: key,

compose/compose_strategy.go

@@ -36,10 +36,11 @@ type CommonStrategy struct {
 	jwt.JWTStrategy
 }
 
-func NewOAuth2HMACStrategy(config *Config, secret []byte) *oauth2.HMACSHAStrategy {
+func NewOAuth2HMACStrategy(config *Config, secret []byte, rotatedSecrets [][]byte) *oauth2.HMACSHAStrategy {
 	return &oauth2.HMACSHAStrategy{
 		Enigma: &hmac.HMACStrategy{
-			GlobalSecret: secret,
+			GlobalSecret:         secret,
+			RotatedGlobalSecrets: rotatedSecrets,
 		},
 		AccessTokenLifespan:   config.GetAccessTokenLifespan(),
 		AuthorizeCodeLifespan: config.GetAuthorizeCodeLifespan(),

token/hmac/hmacsha.go

@@ -37,8 +37,9 @@ import (
 
 // HMACStrategy is responsible for generating and validating challenges.
 type HMACStrategy struct {
-	AuthCodeEntropy int
-	GlobalSecret    []byte
+	AuthCodeEntropy      int
+	GlobalSecret         []byte
+	RotatedGlobalSecrets [][]byte
 	sync.Mutex
 }
 
@@ -59,7 +60,7 @@ func (c *HMACStrategy) Generate() (string, string, error) {
 	defer c.Unlock()
 
 	if len(c.GlobalSecret) < minimumSecretLength {
-		return "", "", errors.Errorf("Secret for signing HMAC-SHA256 is expected to be 32 byte long, got %d byte", len(c.GlobalSecret))
+		return "", "", errors.Errorf("secret for signing HMAC-SHA256 is expected to be 32 byte long, got %d byte", len(c.GlobalSecret))
 	}
 
 	var signingKey [32]byte
@@ -90,12 +91,26 @@ func (c *HMACStrategy) Generate() (string, string, error) {
 
 // Validate validates a token and returns its signature or an error if the token is not valid.
 func (c *HMACStrategy) Validate(token string) error {
-	if len(c.GlobalSecret) < minimumSecretLength {
-		return errors.Errorf("Secret for signing HMAC-SHA256 is expected to be 32 byte long, got %d byte", len(c.GlobalSecret))
+	keys := append([][]byte{c.GlobalSecret}, c.RotatedGlobalSecrets...)
+	for _, key := range keys {
+		if err := c.validate(key, token); err == nil {
+			return nil
+		} else if errors.Cause(err) == fosite.ErrTokenSignatureMismatch {
+		} else {
+			return err
+		}
+	}
+
+	return errors.New("a secret for signing HMAC-SHA256 is expected to be defined, but none were")
+}
+
+func (c *HMACStrategy) validate(secret []byte, token string) error {
+	if len(secret) < minimumSecretLength {
+		return errors.Errorf("secret for signing HMAC-SHA256 is expected to be 32 byte long, got %d byte", len(secret))
 	}
 
 	var signingKey [32]byte
-	copy(signingKey[:], c.GlobalSecret)
+	copy(signingKey[:], secret)
 
 	split := strings.Split(token, ".")
 	if len(split) != 2 {

token/hmac/hmacsha_test.go

@@ -75,3 +75,46 @@ func TestValidateSignatureRejects(t *testing.T) {
 		t.Logf("Passed test case %d", k)
 	}
 }
+
+func TestValidateWithRotatedKey(t *testing.T) {
+	old := HMACStrategy{
+		GlobalSecret: []byte("1234567890123456789012345678901234567890"),
+	}
+	now := HMACStrategy{
+		GlobalSecret: []byte("0000000090123456789012345678901234567890"),
+		RotatedGlobalSecrets: [][]byte{
+			[]byte("abcdefgh90123456789012345678901234567890"),
+			[]byte("1234567890123456789012345678901234567890"),
+		},
+	}
+
+	token, _, err := old.Generate()
+	require.NoError(t, err)
+
+	require.NoError(t, now.Validate(token))
+}
+
+func TestValidateWithRotatedKeyInvalid(t *testing.T) {
+	old := HMACStrategy{
+		GlobalSecret: []byte("1234567890123456789012345678901234567890"),
+	}
+	now := HMACStrategy{
+		GlobalSecret: []byte("0000000090123456789012345678901234567890"),
+		RotatedGlobalSecrets: [][]byte{
+			[]byte("abcdefgh90123456789012345678901"),
+			[]byte("1234567890123456789012345678901234567890"),
+		},
+	}
+
+	token, _, err := old.Generate()
+	require.NoError(t, err)
+
+	require.Error(t, now.Validate(token))
+
+	now = HMACStrategy{
+		GlobalSecret:         nil,
+		RotatedGlobalSecrets: [][]byte{},
+	}
+
+	require.Error(t, now.Validate(token))
+}