Add TokenManager for API token generation and hashing

3 files changed, 111 insertions, 0 deletions

diff --git a/player-server/internal/auth/interfaces.go b/player-server/internal/auth/interfaces.go
index 3b6ea67..790c534 100644
--- a/player-server/internal/auth/interfaces.go
+++ b/player-server/internal/auth/interfaces.go
@@ -13,3 +13,9 @@ type SessionManager interface {
 	DeleteSession(ctx context.Context, id string) error
 	Cleanup(ctx context.Context) error
 }
+
+// TokenManager is the abstraction for API token generation and hashing.
+type TokenManager interface {
+	Generate() (plaintext, hash string)
+	Hash(plaintext string) string
+}
diff --git a/player-server/internal/auth/token.go b/player-server/internal/auth/token.go
new file mode 100644
index 0000000..bdb7e6b
--- /dev/null
+++ b/player-server/internal/auth/token.go
@@ -0,0 +1,39 @@
+package auth
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+)
+
+const tokenByteLength = 32
+
+// Compile-time check that *tokenManager satisfies the TokenManager interface.
+var _ TokenManager = (*tokenManager)(nil)
+
+type tokenManager struct{}
+
+// NewTokenManager creates a TokenManager.
+func NewTokenManager() TokenManager {
+	return &tokenManager{}
+}
+
+// Generate creates a plaintext API token and its stored hash.
+func (m *tokenManager) Generate() (plaintext, hash string) {
+	b := make([]byte, tokenByteLength)
+	if _, err := rand.Read(b); err != nil {
+		panic(fmt.Sprintf("generate token: %v", err))
+	}
+
+	plaintext = hex.EncodeToString(b)
+	return plaintext, m.Hash(plaintext)
+}
+
+// Hash returns the SHA-256 hash of a plaintext API token.
+func (m *tokenManager) Hash(plaintext string) string {
+	// SHA-256 is used instead of bcrypt because API tokens are high-entropy
+	// random bytes; bcrypt adds CPU cost without meaningful security benefit.
+	sum := sha256.Sum256([]byte(plaintext))
+	return hex.EncodeToString(sum[:])
+}
diff --git a/player-server/internal/auth/token_test.go b/player-server/internal/auth/token_test.go
new file mode 100644
index 0000000..bf18aa5
--- /dev/null
+++ b/player-server/internal/auth/token_test.go
@@ -0,0 +1,66 @@
+package auth
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"testing"
+)
+
+func TestTokenManager_Generate(t *testing.T) {
+	tm := NewTokenManager()
+	seen := make(map[string]string)
+
+	for i := 0; i < 1000; i++ {
+		plaintext, hash := tm.Generate()
+		if len(plaintext) != tokenByteLength*2 {
+			t.Fatalf("expected plaintext length %d, got %d", tokenByteLength*2, len(plaintext))
+		}
+		decoded, err := hex.DecodeString(plaintext)
+		if err != nil {
+			t.Fatalf("expected hex plaintext: %v", err)
+		}
+		if len(decoded) != tokenByteLength {
+			t.Fatalf("expected %d decoded bytes, got %d", tokenByteLength, len(decoded))
+		}
+		if hash != tm.Hash(plaintext) {
+			t.Fatal("expected hash to match plaintext")
+		}
+		if previousHash, ok := seen[plaintext]; ok {
+			t.Fatalf("duplicate token generated with hashes %q and %q", previousHash, hash)
+		}
+		seen[plaintext] = hash
+	}
+}
+
+func TestTokenManager_Hash(t *testing.T) {
+	tm := NewTokenManager()
+	tests := []struct {
+		name      string
+		plaintext string
+	}{
+		{"empty token", ""},
+		{"hex token", "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"},
+		{"plain string", "api-token"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			hash := tm.Hash(tt.plaintext)
+			if hash == "" {
+				t.Fatal("expected non-empty hash")
+			}
+			if len(hash) != sha256.Size*2 {
+				t.Fatalf("expected hash length %d, got %d", sha256.Size*2, len(hash))
+			}
+			if _, err := hex.DecodeString(hash); err != nil {
+				t.Fatalf("expected hex hash: %v", err)
+			}
+			if hash != tm.Hash(tt.plaintext) {
+				t.Fatal("expected deterministic hash")
+			}
+			if tt.plaintext != "" && hash == tm.Hash(tt.plaintext+"x") {
+				t.Fatal("expected different plaintext to have different hash")
+			}
+		})
+	}
+}