FEAT: Add ActiveDirectoryMSI support for bulk copy (#573)

Author: bewithgaurav

mssql_python/auth.py

@@ -11,15 +11,33 @@
 
 from mssql_python.logging import logger
 from mssql_python.constants import AuthType, ConstantsDDBC
+from mssql_python.connection_string_parser import _ConnectionStringParser
 
 # Module-level credential instance cache.
 # Reusing credential objects allows the Azure Identity SDK's built-in
 # in-memory token cache to work, avoiding redundant token acquisitions.
 # See: https://github.com/Azure/azure-sdk-for-python/blob/main/sdk/identity/azure-identity/TOKEN_CACHING.md
-_credential_cache: Dict[str, object] = {}
+#
+# Cache is keyed on (auth_type, sorted credential_kwargs), which is
+# bounded by the distinct credentials a single process ever uses.
+_credential_cache: Dict[object, object] = {}
 _credential_cache_lock = threading.Lock()
 
 
+def _credential_cache_key(auth_type: str, credential_kwargs: Optional[Dict[str, str]]):
+    """Build a hashable cache key from auth_type and optional credential kwargs.
+
+    Returns the plain auth_type string when no kwargs are provided so that
+    callers caching by string (the original behavior) keep working. When
+    kwargs are present (e.g. user-assigned MSI client_id), the key is a
+    tuple of ``(auth_type, sorted_kwargs_items)`` so different kwargs map
+    to different cached credentials.
+    """
+    if not credential_kwargs:
+        return auth_type
+    return (auth_type, tuple(sorted(credential_kwargs.items())))
+
+
 class AADAuth:
     """Handles Azure Active Directory authentication"""
 
@@ -37,24 +55,26 @@ def get_token_struct(token: str) -> bytes:
         return struct.pack(f"<I{len(token_bytes)}s", len(token_bytes), token_bytes)
 
     @staticmethod
-    def get_token(auth_type: str) -> bytes:
+    def get_token(auth_type: str, credential_kwargs: Optional[Dict[str, str]] = None) -> bytes:
         """Get DDBC token struct for the specified authentication type."""
-        token_struct, _ = AADAuth._acquire_token(auth_type)
+        token_struct, _ = AADAuth._acquire_token(auth_type, credential_kwargs)
         return token_struct
 
     @staticmethod
-    def get_raw_token(auth_type: str) -> str:
+    def get_raw_token(auth_type: str, credential_kwargs: Optional[Dict[str, str]] = None) -> str:
         """Acquire a raw JWT for the mssql-py-core connection (bulk copy).
 
         Uses the cached credential instance so the Azure Identity SDK's
         built-in token cache can serve a valid token without a round-trip
         when the previous token has not yet expired.
         """
-        _, raw_token = AADAuth._acquire_token(auth_type)
+        _, raw_token = AADAuth._acquire_token(auth_type, credential_kwargs)
         return raw_token
 
     @staticmethod
-    def _acquire_token(auth_type: str) -> Tuple[bytes, str]:
+    def _acquire_token(
+        auth_type: str, credential_kwargs: Optional[Dict[str, str]] = None
+    ) -> Tuple[bytes, str]:
         """Internal: acquire token and return (ddbc_struct, raw_jwt)."""
         # Import Azure libraries inside method to support test mocking
         # pylint: disable=import-outside-toplevel
@@ -63,6 +83,7 @@ def _acquire_token(auth_type: str) -> Tuple[bytes, str]:
                 DefaultAzureCredential,
                 DeviceCodeCredential,
                 InteractiveBrowserCredential,
+                ManagedIdentityCredential,
             )
             from azure.core.exceptions import ClientAuthenticationError
         except ImportError as e:
@@ -76,6 +97,7 @@ def _acquire_token(auth_type: str) -> Tuple[bytes, str]:
             "default": DefaultAzureCredential,
             "devicecode": DeviceCodeCredential,
             "interactive": InteractiveBrowserCredential,
+            "msi": ManagedIdentityCredential,
         }
 
         credential_class = credential_map.get(auth_type)
@@ -89,20 +111,22 @@ def _acquire_token(auth_type: str) -> Tuple[bytes, str]:
             credential_class.__name__,
         )
 
+        kwargs = credential_kwargs or {}
+        cache_key = _credential_cache_key(auth_type, kwargs)
         try:
             with _credential_cache_lock:
-                if auth_type not in _credential_cache:
+                if cache_key not in _credential_cache:
                     logger.debug(
                         "get_token: Creating new credential instance for auth_type=%s",
                         auth_type,
                     )
-                    _credential_cache[auth_type] = credential_class()
+                    _credential_cache[cache_key] = credential_class(**kwargs)
                 else:
                     logger.debug(
                         "get_token: Reusing cached credential instance for auth_type=%s",
                         auth_type,
                     )
-                credential = _credential_cache[auth_type]
+                credential = _credential_cache[cache_key]
             raw_token = credential.get_token("https://database.windows.net/.default").token
             logger.info(
                 "get_token: Azure AD token acquired successfully - token_length=%d chars",
@@ -130,6 +154,28 @@ def _acquire_token(auth_type: str) -> Tuple[bytes, str]:
             raise RuntimeError(f"Failed to create {credential_class.__name__}: {e}") from e
 
 
+def _extract_msi_client_id(connection_string: str) -> Optional[str]:
+    """Pull UID out of a connection string for user-assigned MSI.
+
+    For ActiveDirectoryMSI, UID (when present) carries the user-assigned
+    identity's ``client_id``. Returns None for system-assigned MSI.
+
+    Uses the canonical ``_ConnectionStringParser`` so braced ODBC values
+    are handled correctly: a ``UID={hello=world}`` resolves to the value
+    ``hello=world`` (no surrounding braces, no false split on the inner
+    ``=``), and a semicolon inside a legitimate braced value (e.g.
+    ``Database={foo;uid=victim;bar}``) cannot spoof a top-level ``UID=``.
+    """
+    # Connection.__init__ already parsed the same string through
+    # _ConnectionStringParser via _construct_connection_string, so by the
+    # time we get here the input is guaranteed parseable. No defensive
+    # try/except: a parse failure now means a real bug upstream and should
+    # propagate, not silently degrade user-assigned MSI to system-assigned.
+    parsed = _ConnectionStringParser(validate_keywords=False)._parse(connection_string)
+    uid = (parsed.get("uid") or "").strip()
+    return uid or None
+
+
 def process_auth_parameters(parameters: List[str]) -> Tuple[List[str], Optional[str]]:
     """
     Process connection parameters and extract authentication type.
@@ -180,6 +226,10 @@ def process_auth_parameters(parameters: List[str]) -> Tuple[List[str], Optional[
                 # Default authentication (uses DefaultAzureCredential)
                 logger.debug("process_auth_parameters: Default Azure authentication detected")
                 auth_type = "default"
+            elif value_lower == AuthType.MSI.value:
+                # Managed identity authentication (system- or user-assigned)
+                logger.debug("process_auth_parameters: Managed identity authentication detected")
+                auth_type = "msi"
         modified_parameters.append(param)
 
     logger.debug(
@@ -212,7 +262,9 @@ def remove_sensitive_params(parameters: List[str]) -> List[str]:
     return result
 
 
-def get_auth_token(auth_type: str) -> Optional[bytes]:
+def get_auth_token(
+    auth_type: str, credential_kwargs: Optional[Dict[str, str]] = None
+) -> Optional[bytes]:
     """Get DDBC authentication token struct based on auth type."""
     logger.debug("get_auth_token: Starting - auth_type=%s", auth_type)
     if not auth_type:
@@ -225,7 +277,7 @@ def get_auth_token(auth_type: str) -> Optional[bytes]:
         return None  # Let Windows handle AADInteractive natively
 
     try:
-        token = AADAuth.get_token(auth_type)
+        token = AADAuth.get_token(auth_type, credential_kwargs)
         logger.info("get_auth_token: Token acquired successfully - auth_type=%s", auth_type)
         return token
     except (ValueError, RuntimeError) as e:
@@ -246,6 +298,7 @@ def extract_auth_type(connection_string: str) -> Optional[str]:
         AuthType.INTERACTIVE.value: "interactive",
         AuthType.DEVICE_CODE.value: "devicecode",
         AuthType.DEFAULT.value: "default",
+        AuthType.MSI.value: "msi",
     }
     for part in connection_string.split(";"):
         key, _, value = part.strip().partition("=")
@@ -256,16 +309,28 @@ def extract_auth_type(connection_string: str) -> Optional[str]:
 
 def process_connection_string(
     connection_string: str,
-) -> Tuple[str, Optional[Dict[int, bytes]], Optional[str]]:
+) -> Tuple[str, Optional[Dict[int, bytes]], Optional[str], Optional[Dict[str, str]]]:
     """
     Process connection string and handle authentication.
 
+    NOTE: Returns a 4-tuple. Callers must unpack all four elements.
+    Destructuring with three names raises ``ValueError: too many values
+    to unpack``. The fourth element (``credential_kwargs``) is needed by
+    Connection.__init__ to persist credential constructor args (e.g. the
+    user-assigned MSI ``client_id``) for the bulkcopy fresh-token path,
+    since UID is stripped from the sanitized connection string.
+
     Args:
         connection_string: The connection string to process
 
     Returns:
-        Tuple[str, Optional[Dict], Optional[str]]: Processed connection string,
-            attrs_before dict if needed, and auth_type string for bulk copy token acquisition
+        Tuple[str, Optional[Dict], Optional[str], Optional[Dict[str, str]]]:
+            Processed connection string, attrs_before dict if needed, auth_type
+            string for bulk copy token acquisition, and credential constructor
+            kwargs (e.g. user-assigned MSI ``client_id``) to be persisted on
+            the Connection so bulkcopy can re-use them when acquiring a fresh
+            token after sanitization has stripped UID from the connection
+            string.
 
     Raises:
         ValueError: If the connection string is invalid or empty
@@ -301,12 +366,33 @@ def process_connection_string(
 
     modified_parameters, auth_type = process_auth_parameters(parameters)
 
+    # Capture credential kwargs (e.g. user-assigned MSI client_id) before
+    # remove_sensitive_params strips UID from the parameter list. Pass the
+    # original connection_string (not modified_parameters) so the helper can
+    # use the canonical _ConnectionStringParser — handles braced values like
+    # UID={hello=world} correctly.
+    credential_kwargs: Dict[str, str] = {}
+    if auth_type == "msi":
+        client_id = _extract_msi_client_id(connection_string)
+        if client_id:
+            credential_kwargs["client_id"] = client_id
+            logger.debug(
+                "process_connection_string: ActiveDirectoryMSI with UID — "
+                "user-assigned managed identity selected (client_id length=%d)",
+                len(client_id),
+            )
+        else:
+            logger.debug(
+                "process_connection_string: ActiveDirectoryMSI without UID — "
+                "system-assigned managed identity selected"
+            )
+
     if auth_type:
         logger.info(
             "process_connection_string: Authentication type detected - auth_type=%s", auth_type
         )
         modified_parameters = remove_sensitive_params(modified_parameters)
-        token_struct = get_auth_token(auth_type)
+        token_struct = get_auth_token(auth_type, credential_kwargs or None)
         if token_struct:
             logger.info(
                 "process_connection_string: Token authentication configured successfully - auth_type=%s",
@@ -316,6 +402,7 @@ def process_connection_string(
                 ";".join(modified_parameters) + ";",
                 {ConstantsDDBC.SQL_COPT_SS_ACCESS_TOKEN.value: token_struct},
                 auth_type,
+                credential_kwargs or None,
             )
         else:
             logger.warning(
@@ -326,4 +413,9 @@ def process_connection_string(
         "process_connection_string: Connection string processing complete - has_auth=%s",
         bool(auth_type),
     )
-    return ";".join(modified_parameters) + ";", None, auth_type
+    return (
+        ";".join(modified_parameters) + ";",
+        None,
+        auth_type,
+        credential_kwargs or None,
+    )

mssql_python/connection.py

@@ -321,6 +321,12 @@ def __init__(
         # We intentionally do NOT cache the token — a fresh one is acquired
         # each time bulkcopy() is called to avoid expired-token errors.
         self._auth_type = None
+        # Credential constructor kwargs (e.g. user-assigned MSI client_id)
+        # captured at __init__ time before remove_sensitive_params strips UID
+        # from self.connection_str. bulkcopy() re-uses these when acquiring a
+        # fresh token; re-parsing self.connection_str at that point would miss
+        # them because UID is already gone.
+        self._credential_kwargs: Optional[Dict[str, str]] = None
 
         # Check if the connection string contains authentication parameters
         # This is important for processing the connection string correctly.
@@ -335,6 +341,7 @@ def __init__(
             # On Windows Interactive, process_connection_string returns None
             # (DDBC handles auth natively), so fall back to the connection string.
             self._auth_type = connection_result[2] or extract_auth_type(self.connection_str)
+            self._credential_kwargs = connection_result[3]
 
         self._closed = False
         self._timeout = timeout

mssql_python/constants.py

@@ -337,6 +337,7 @@ class AuthType(Enum):
     INTERACTIVE = "activedirectoryinteractive"
     DEVICE_CODE = "activedirectorydevicecode"
     DEFAULT = "activedirectorydefault"
+    MSI = "activedirectorymsi"
 
 
 class SQLTypes:

mssql_python/cursor.py

@@ -2933,11 +2933,17 @@ def bulkcopy(
 
         # Token acquisition — only thing cursor must handle (needs azure-identity SDK)
         if self.connection._auth_type:
-            # Fresh token acquisition for mssql-py-core connection
+            # Fresh token acquisition for mssql-py-core connection. credential
+            # kwargs (e.g. user-assigned MSI client_id) were captured by
+            # Connection.__init__ before remove_sensitive_params stripped UID
+            # from connection_str — re-parsing here would miss them.
             from mssql_python.auth import AADAuth
 
             try:
-                raw_token = AADAuth.get_raw_token(self.connection._auth_type)
+                raw_token = AADAuth.get_raw_token(
+                    self.connection._auth_type,
+                    self.connection._credential_kwargs,
+                )
             except (RuntimeError, ValueError) as e:
                 raise RuntimeError(
                     f"Bulk copy failed: unable to acquire Azure AD token "