kes: add support for API key authentication

This commit adds support for KES<->KES authentication
via API keys. Now, a KES edge server can authenticate
to a KES server (stateful) via API keys - not just
via TLS private key / certificate files.

internal/keystore/kes/kes.go

@@ -30,6 +30,11 @@ type Config struct {
 	// If empty, the default enclave is used.
 	Enclave string
 
+	// APIKey is an API key to authenticate to the
+	// KES server. Either an API key or a mTLS private
+	// key and certificate can be used for authentication.
+	APIKey kes.APIKey
+
 	// PrivateKey is a path to a file containing
 	// a X.509 private key for mTLS authentication.
 	PrivateKey string
@@ -50,17 +55,34 @@ func Connect(ctx context.Context, config *Config) (*Conn, error) {
 	if len(config.Endpoints) == 0 {
 		return nil, errors.New("kes: no endpoints provided")
 	}
-	if config.Certificate == "" {
-		return nil, errors.New("kes: no certificate provided")
-	}
-	if config.PrivateKey == "" {
-		return nil, errors.New("kes: no private key provided")
+	if config.APIKey != nil && (config.PrivateKey != "" || config.Certificate != "") {
+		return nil, errors.New("kes: ambiguous configuration: API key as well as mTLS private key and certificate provided")
 	}
 
-	cert, err := https.CertificateFromFile(config.Certificate, config.PrivateKey, "")
-	if err != nil {
-		return nil, err
+	var (
+		err  error
+		cert tls.Certificate
+	)
+	switch {
+	case config.APIKey != nil:
+		cert, err = kes.GenerateCertificate(config.APIKey)
+		if err != nil {
+		}
+	case config.PrivateKey != "" || config.Certificate != "":
+		if config.Certificate == "" {
+			return nil, errors.New("kes: no certificate provided")
+		}
+		if config.PrivateKey == "" {
+			return nil, errors.New("kes: no private key provided")
+		}
+		cert, err = https.CertificateFromFile(config.Certificate, config.PrivateKey, "")
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, errors.New("kes: no API key nor private key and certificate provided")
 	}
+
 	var rootCAs *x509.CertPool
 	if config.CAPath != "" {
 		rootCAs, err = https.CertPoolFromFile(config.CAPath)

keserv/config.go

@@ -337,6 +337,10 @@ type KESConfig struct {
 	// the default enclave name will be used.
 	Enclave Env[string]
 
+	// APIKey is an API key to authenticate to the
+	// KES server.
+	APIKey Env[string]
+
 	// CertificateFile is a path to a mTLS client
 	// certificate file used to authenticate to
 	// the KES server.
@@ -362,9 +366,19 @@ func (c *KESConfig) Connect(ctx context.Context) (kms.Conn, error) {
 	for _, endpoint := range c.Endpoints {
 		endpoints = append(endpoints, endpoint.Value)
 	}
+
+	var key kes.APIKey
+	if c.APIKey.Value != "" {
+		k, err := kes.ParseAPIKey(c.APIKey.Value)
+		if err != nil {
+			return nil, err
+		}
+		key = k
+	}
 	return kesstore.Connect(ctx, &kesstore.Config{
 		Endpoints:   endpoints,
 		Enclave:     c.Enclave.Value,
+		APIKey:      key,
 		Certificate: c.CertificateFile.Value,
 		PrivateKey:  c.PrivateKeyFile.Value,
 		CAPath:      c.CAPath.Value,
@@ -373,6 +387,7 @@ func (c *KESConfig) Connect(ctx context.Context) (kms.Conn, error) {
 
 func (c *KESConfig) toYAML(yml *serverConfigYAML) {
 	yml.KeyStore.KES.Endpoint = c.Endpoints
+	yml.KeyStore.KES.APIKey = c.APIKey
 	yml.KeyStore.KES.TLS.Certificate = c.CertificateFile
 	yml.KeyStore.KES.TLS.PrivateKey = c.PrivateKeyFile
 	yml.KeyStore.KES.TLS.CAPath = c.CAPath
@@ -381,6 +396,7 @@ func (c *KESConfig) toYAML(yml *serverConfigYAML) {
 func (c *KESConfig) fromYAML(yml *serverConfigYAML) {
 	c.Endpoints = yml.KeyStore.KES.Endpoint
 	c.Enclave = yml.KeyStore.KES.Enclave
+	c.APIKey = yml.KeyStore.KES.APIKey
 	c.CertificateFile = yml.KeyStore.KES.TLS.Certificate
 	c.PrivateKeyFile = yml.KeyStore.KES.TLS.PrivateKey
 	c.CAPath = yml.KeyStore.KES.TLS.CAPath

keserv/yml.go

@@ -64,6 +64,7 @@ type serverConfigYAML struct {
 		KES struct {
 			Endpoint []Env[string] `yaml:"endpoint,omitempty"`
 			Enclave  Env[string]   `yaml:"enclave,omitempty"`
+			APIKey   Env[string]   `yaml:"api_key,omitempty"`
 			TLS      struct {
 				Certificate Env[string] `yaml:"cert,omitempty"`
 				PrivateKey  Env[string] `yaml:"key,omitempty"`

server-config.yaml

@@ -189,6 +189,7 @@ keystore:
     endpoint: 
     - ""           # The endpoint (or list of endpoints) to the KES server(s)
     enclave: ""    # An optional enclave name. If empty, the default enclave will be used
+    api_key: ""    # The KES API key to authenticate to KES server
     tls:           # The KES mTLS authentication credentials - i.e. client certificate.
       cert: ""     # Path to the TLS client certificate for mTLS authentication
       key: ""      # Path to the TLS client private key for mTLS authentication