package server import ( "context" "crypto/rand" "crypto/rsa" "encoding/hex" "errors" "fmt" "io" "time" "gopkg.in/square/go-jose.v2" "github.com/dexidp/dex/pkg/log" "github.com/dexidp/dex/storage" ) var errAlreadyRotated = errors.New("keys already rotated by another server instance") // rotationStrategy describes a strategy for generating cryptographic keys, how // often to rotate them, and how long they can validate signatures after rotation. type rotationStrategy struct { // Time between rotations. rotationFrequency time.Duration // After being rotated how long should the key be kept around for validating // signatues? idTokenValidFor time.Duration // Keys are always RSA keys. Though cryptopasta recommends ECDSA keys, not every // client may support these (e.g. github.com/coreos/go-oidc/oidc). key func() (*rsa.PrivateKey, error) } // staticRotationStrategy returns a strategy which never rotates keys. func staticRotationStrategy(key *rsa.PrivateKey) rotationStrategy { return rotationStrategy{ // Setting these values to 100 years is easier than having a flag indicating no rotation. rotationFrequency: time.Hour * 8760 * 100, idTokenValidFor: time.Hour * 8760 * 100, key: func() (*rsa.PrivateKey, error) { return key, nil }, } } // defaultRotationStrategy returns a strategy which rotates keys every provided period, // holding onto the public parts for some specified amount of time. func defaultRotationStrategy(rotationFrequency, idTokenValidFor time.Duration) rotationStrategy { return rotationStrategy{ rotationFrequency: rotationFrequency, idTokenValidFor: idTokenValidFor, key: func() (*rsa.PrivateKey, error) { return rsa.GenerateKey(rand.Reader, 2048) }, } } type keyRotator struct { storage.Storage strategy rotationStrategy now func() time.Time logger log.Logger } // startKeyRotation begins key rotation in a new goroutine, closing once the context is canceled. // // The method blocks until after the first attempt to rotate keys has completed. That way // healthy storages will return from this call with valid keys. func (s *Server) startKeyRotation(ctx context.Context, strategy rotationStrategy, now func() time.Time) { rotator := keyRotator{s.storage, strategy, now, s.logger} // Try to rotate immediately so properly configured storages will have keys. if err := rotator.rotate(); err != nil { if err == errAlreadyRotated { s.logger.Infof("Key rotation not needed: %v", err) } else { s.logger.Errorf("failed to rotate keys: %v", err) } } go func() { for { select { case <-ctx.Done(): return case <-time.After(time.Second * 30): if err := rotator.rotate(); err != nil { s.logger.Errorf("failed to rotate keys: %v", err) } } } }() } func (k keyRotator) rotate() error { keys, err := k.GetKeys() if err != nil && err != storage.ErrNotFound { return fmt.Errorf("get keys: %v", err) } if k.now().Before(keys.NextRotation) { return nil } k.logger.Infof("keys expired, rotating") // Generate the key outside of a storage transaction. key, err := k.strategy.key() if err != nil { return fmt.Errorf("generate key: %v", err) } b := make([]byte, 20) if _, err := io.ReadFull(rand.Reader, b); err != nil { panic(err) } keyID := hex.EncodeToString(b) priv := &jose.JSONWebKey{ Key: key, KeyID: keyID, Algorithm: "RS256", Use: "sig", } pub := &jose.JSONWebKey{ Key: key.Public(), KeyID: keyID, Algorithm: "RS256", Use: "sig", } var nextRotation time.Time err = k.Storage.UpdateKeys(func(keys storage.Keys) (storage.Keys, error) { tNow := k.now() // if you are running multiple instances of dex, another instance // could have already rotated the keys. if tNow.Before(keys.NextRotation) { return storage.Keys{}, errAlreadyRotated } expired := func(key storage.VerificationKey) bool { return tNow.After(key.Expiry) } // Remove any verification keys that have expired. i := 0 for _, key := range keys.VerificationKeys { if !expired(key) { keys.VerificationKeys[i] = key i++ } } keys.VerificationKeys = keys.VerificationKeys[:i] if keys.SigningKeyPub != nil { // Move current signing key to a verification only key, throwing // away the private part. verificationKey := storage.VerificationKey{ PublicKey: keys.SigningKeyPub, // After demoting the signing key, keep the token around for at least // the amount of time an ID Token is valid for. This ensures the // verification key won't expire until all ID Tokens it's signed // expired as well. Expiry: tNow.Add(k.strategy.idTokenValidFor), } keys.VerificationKeys = append(keys.VerificationKeys, verificationKey) } nextRotation = k.now().Add(k.strategy.rotationFrequency) keys.SigningKey = priv keys.SigningKeyPub = pub keys.NextRotation = nextRotation return keys, nil }) if err != nil { return err } k.logger.Infof("keys rotated, next rotation: %s", nextRotation) return nil }