URL-encode client_id in Azure IMDS token request

The `_get_azure_response()` function constructs the Azure IMDS URL by
interpolating `client_id` via f-string without URL encoding. While
`resource` is already encoded (via `quote()` at the call site in
`auth_oidc_shared.py`), `client_id` is not, creating an inconsistency.

Apply `urllib.parse.quote()` to `client_id` before interpolation,
consistent with the handling of `resource` and with the Node.js driver's
use of `url.searchParams.append()` for the same parameter.

Add a test to verify special characters in `client_id` are properly
percent-encoded and cannot introduce additional query parameters.

pymongo/_azure_helpers.py

@@ -17,6 +17,7 @@ from __future__ import annotations
 
 import json
 from typing import Any, Optional
+from urllib.parse import quote
 
 
 def _get_azure_response(
@@ -29,7 +30,7 @@ def _get_azure_response(
     url += "?api-version=2018-02-01"
     url += f"&resource={resource}"
     if client_id:
-        url += f"&client_id={client_id}"
+        url += f"&client_id={quote(client_id)}"
     headers = {"Metadata": "true", "Accept": "application/json"}
     request = Request(url, headers=headers)  # noqa: S310
     try:

test/test_azure_helpers.py

@@ -150,6 +150,20 @@ class TestGetAzureResponse(unittest.TestCase):
         _, kwargs = mock_open.call_args
         self.assertEqual(kwargs["timeout"], 42)
 
+    def test_client_id_is_url_encoded(self):
+        """Ensure special characters in client_id are percent-encoded."""
+        body = json.dumps({"access_token": "tok", "expires_in": "3600"})
+        with _mock_urlopen(200, body) as mock_open:
+            self._call(client_id="id with spaces&special=chars")
+
+        url = mock_open.call_args[0][0].full_url
+        # '&' and '=' must be percent-encoded so they don't inject extra query params
+        self.assertIn("client_id=id%20with%20spaces%26special%3Dchars", url)
+        # The encoded client_id should not introduce a raw '&'
+        # Count params: api-version, resource, client_id — exactly 3
+        query_string = url.split("?", 1)[1]
+        self.assertEqual(query_string.count("&"), 2)
+
 
 if __name__ == "__main__":
     unittest.main()