feat: pinned master key TLS and per-agent tokens

internal/agenttoken/agenttoken.go

@@ -0,0 +1,31 @@
+// Package agenttoken creates and hashes the per-agent tokens agents present
+// to the master.
+package agenttoken
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/hex"
+	"fmt"
+)
+
+const prefix = "pua_"
+
+// Generate returns a new random agent token. Show it to the operator once;
+// store only Hash(token).
+func Generate() (string, error) {
+	var b [32]byte
+	if _, err := rand.Read(b[:]); err != nil {
+		return "", fmt.Errorf("generate agent token: %w", err)
+	}
+	return prefix + base64.RawURLEncoding.EncodeToString(b[:]), nil
+}
+
+// Hash returns the value stored for token. A plain SHA-256 is sufficient
+// because tokens carry 256 bits of randomness; salting protects low-entropy
+// passwords, which these are not.
+func Hash(token string) string {
+	sum := sha256.Sum256([]byte(token))
+	return hex.EncodeToString(sum[:])
+}

internal/agenttoken/agenttoken_test.go

@@ -0,0 +1,25 @@
+package agenttoken
+
+import (
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGenerate(t *testing.T) {
+	a, err := Generate()
+	require.NoError(t, err)
+	b, err := Generate()
+	require.NoError(t, err)
+
+	assert.Regexp(t, regexp.MustCompile(`^pua_[A-Za-z0-9_-]{43}$`), a)
+	assert.NotEqual(t, a, b)
+}
+
+func TestHash(t *testing.T) {
+	assert.Equal(t, Hash("pua_x"), Hash("pua_x"))
+	assert.NotEqual(t, Hash("pua_x"), Hash("pua_y"))
+	assert.Regexp(t, regexp.MustCompile(`^[0-9a-f]{64}$`), Hash("pua_x"))
+}