feat: add security module (encryption + auth)

- Implement AES-256-GCM encryption for sensitive data
- Implement decryption function
- Implement Bearer token authentication verification
- Add comprehensive tests for encryption/decryption roundtrip
- Add tests for API token verification (success and failure cases)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/security.py

@@ -0,0 +1,78 @@
+import base64
+import os
+from typing import Optional
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+from cryptography.hazmat.backends import default_backend
+
+
+def encrypt_data(data: bytes, key_b64: str) -> bytes:
+    """
+    使用 AES-256-GCM 加密数据.
+
+    Args:
+        data: 原始数据
+        key_b64: Base64 编码的加密密钥
+
+    Returns:
+        加密后的数据 (nonce + ciphertext + tag)
+    """
+    key = base64.b64decode(key_b64)
+    nonce = os.urandom(12)  # GCM 96-bit nonce
+
+    cipher = Cipher(
+        algorithms.AES(key),
+        modes.GCM(nonce),
+        backend=default_backend()
+    )
+    encryptor = cipher.encryptor()
+    ciphertext = encryptor.update(data) + encryptor.finalize()
+
+    # 返回 nonce + ciphertext + tag
+    return nonce + ciphertext + encryptor.tag
+
+
+def decrypt_data(encrypted_data: bytes, key_b64: str) -> bytes:
+    """
+    解密使用 encrypt_data 加密的数据.
+
+    Args:
+        encrypted_data: 加密数据 (nonce + ciphertext + tag)
+        key_b64: Base64 编码的加密密钥
+
+    Returns:
+        解密后的原始数据
+    """
+    key = base64.b64decode(key_b64)
+    nonce = encrypted_data[:12]
+    tag = encrypted_data[-16:]
+    ciphertext = encrypted_data[12:-16]
+
+    cipher = Cipher(
+        algorithms.AES(key),
+        modes.GCM(nonce, tag),
+        backend=default_backend()
+    )
+    decryptor = cipher.decryptor()
+    return decryptor.update(ciphertext) + decryptor.finalize()
+
+
+def verify_api_token(authorization: Optional[str]) -> bool:
+    """
+    验证 Bearer Token.
+
+    Args:
+        authorization: Authorization 头部值
+
+    Returns:
+        Token 是否有效
+    """
+    if not authorization:
+        return False
+
+    if not authorization.startswith('Bearer '):
+        return False
+
+    from app.config import get_settings
+    settings = get_settings()
+    token = authorization[7:]  # 移除 'Bearer ' 前缀
+    return token == settings.api_token

backend/tests/test_security.py

@@ -0,0 +1,34 @@
+import base64
+import pytest
+
+
+def test_encrypt_decrypt_roundtrip():
+    """测试加密解密往返."""
+    from app.security import encrypt_data, decrypt_data
+
+    original = b"sensitive-secret-data"
+    key = base64.b64encode(b'12345678901234567890123456789012').decode()
+
+    encrypted = encrypt_data(original, key)
+    assert encrypted != original
+    assert isinstance(encrypted, bytes)
+    assert len(encrypted) > len(original)  # nonce + ciphertext + tag
+
+    decrypted = decrypt_data(encrypted, key)
+    assert decrypted == original
+
+
+def test_verify_api_token_success(test_env_vars):
+    """测试 API token 验证成功."""
+    from app.security import verify_api_token
+
+    assert verify_api_token("Bearer test-token") is True
+
+
+def test_verify_api_token_failure():
+    """测试 API token 验证失败."""
+    from app.security import verify_api_token
+
+    assert verify_api_token("Bearer wrong-token") is False
+    assert verify_api_token(None) is False
+    assert verify_api_token("Basic token") is False