Add Nix flake for mciasctl and mciasgrpcctl

Vendor dependencies and expose control program binaries via
nix build. Uses nixpkgs-unstable for Go 1.26 support.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/github.com/golang-jwt/jwt/v5/ecdsa_utils.go

@@ -0,0 +1,69 @@
+package jwt
+
+import (
+	"crypto/ecdsa"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+)
+
+var (
+	ErrNotECPublicKey  = errors.New("key is not a valid ECDSA public key")
+	ErrNotECPrivateKey = errors.New("key is not a valid ECDSA private key")
+)
+
+// ParseECPrivateKeyFromPEM parses a PEM encoded Elliptic Curve Private Key Structure
+func ParseECPrivateKeyFromPEM(key []byte) (*ecdsa.PrivateKey, error) {
+	var err error
+
+	// Parse PEM block
+	var block *pem.Block
+	if block, _ = pem.Decode(key); block == nil {
+		return nil, ErrKeyMustBePEMEncoded
+	}
+
+	// Parse the key
+	var parsedKey any
+	if parsedKey, err = x509.ParseECPrivateKey(block.Bytes); err != nil {
+		if parsedKey, err = x509.ParsePKCS8PrivateKey(block.Bytes); err != nil {
+			return nil, err
+		}
+	}
+
+	var pkey *ecdsa.PrivateKey
+	var ok bool
+	if pkey, ok = parsedKey.(*ecdsa.PrivateKey); !ok {
+		return nil, ErrNotECPrivateKey
+	}
+
+	return pkey, nil
+}
+
+// ParseECPublicKeyFromPEM parses a PEM encoded PKCS1 or PKCS8 public key
+func ParseECPublicKeyFromPEM(key []byte) (*ecdsa.PublicKey, error) {
+	var err error
+
+	// Parse PEM block
+	var block *pem.Block
+	if block, _ = pem.Decode(key); block == nil {
+		return nil, ErrKeyMustBePEMEncoded
+	}
+
+	// Parse the key
+	var parsedKey any
+	if parsedKey, err = x509.ParsePKIXPublicKey(block.Bytes); err != nil {
+		if cert, err := x509.ParseCertificate(block.Bytes); err == nil {
+			parsedKey = cert.PublicKey
+		} else {
+			return nil, err
+		}
+	}
+
+	var pkey *ecdsa.PublicKey
+	var ok bool
+	if pkey, ok = parsedKey.(*ecdsa.PublicKey); !ok {
+		return nil, ErrNotECPublicKey
+	}
+
+	return pkey, nil
+}