feat: support Active Directory auth for Windows (#131)

* feat: support Active Directory auth for Windows

* rename integrated_security to active_directory_auth

* Update README.md

Author: shubha-rajan

README.md

@@ -127,6 +127,32 @@ connector.connect(
      enable_iam_auth=True,
  )
 ```
+
+### SQL Server Active Directory Authentication
+Active Directory authentication for SQL Server instances is currently only supported on Windows. First, make sure to follow [these steps](https://cloud.google.com/blog/topics/developers-practitioners/creating-sql-server-instance-integrated-active-directory-using-google-cloud-sql) to set up a Managed AD domain and join your Cloud SQL instance to the domain. [See here for more info on Cloud SQL Active Directory integration](https://cloud.google.com/sql/docs/sqlserver/ad).
+
+Once you have followed the steps linked above, you can run the following code to return a connection object:
+```python
+connector.connect(
+    "project:region:instance",
+    "pytds",
+    db="my_database",
+    active_directory_auth=True,
+    server_name="public.[instance].[location].[project].cloudsql.[domain]",
+)
+``` 
+Or, if using Private IP:
+```python
+connector.connect(
+    "project:region:instance",
+    "pytds",
+    db="my_database",
+    active_directory_auth=True,
+    server_name="private.[instance].[location].[project].cloudsql.[domain]",
+    ip_types=IPTypes.PRIVATE
+)
+``` 
+
 ### Setup for development
 
 Tests can be run with `nox`. Change directory into the `cloud-sql-python-connector` and just run `nox` to run the tests.

google/cloud/sql/connector/instance_connection_manager.py

@@ -29,6 +29,7 @@
 from google.auth.credentials import Credentials
 import google.auth.transport.requests
 import OpenSSL
+import platform
 import ssl
 import socket
 from tempfile import TemporaryDirectory
@@ -108,6 +109,15 @@ def __init__(self, *args: Any) -> None:
         super(CloudSQLIPTypeError, self).__init__(self, *args)
 
 
+class PlatformNotSupportedError(Exception):
+    """
+    Raised when a feature is not supported on the current platform.
+    """
+
+    def __init__(self, *args: Any) -> None:
+        super(PlatformNotSupportedError, self).__init__(self, *args)
+
+
 class InstanceMetadata:
     ip_addrs: Dict[str, Any]
     context: ssl.SSLContext
@@ -564,15 +574,31 @@ def _connect_with_pytds(
             raise ImportError(
                 'Unable to import module "pytds." Please install and try again.'
             )
-        user = kwargs.pop("user")
-        db = kwargs.pop("db")
-        passwd = kwargs.pop("password")
+
+        db = kwargs.pop("db", None)
 
         # Create socket and wrap with context.
         sock = ctx.wrap_socket(
             socket.create_connection((ip_address, SERVER_PROXY_PORT)),
             server_hostname=ip_address,
         )
+        if kwargs.pop("active_directory_auth", False):
+            if platform.system() == "Windows":
+                # Ignore username and password if using active directory auth
+                server_name = kwargs.pop("server_name")
+                return pytds.connect(
+                    database=db,
+                    auth=pytds.login.SspiAuth(port=1433, server_name=server_name),
+                    sock=sock,
+                    **kwargs,
+                )
+            else:
+                raise PlatformNotSupportedError(
+                    "Active Directory authentication is currently only supported on Windows."
+                )
+
+        user = kwargs.pop("user")
+        passwd = kwargs.pop("password")
         return pytds.connect(
             ip_address, database=db, user=user, password=passwd, sock=sock, **kwargs
         )