Remove the reliance on socket.getfqdn()

Author: rayluo

msal/managed_identity.py

@@ -6,7 +6,6 @@
 import json
 import logging
 import os
-import socket
 import sys
 import time
 from urllib.parse import urlparse # Python 3+
@@ -146,7 +145,10 @@ class ManagedIdentityClient(object):
  (like what a ``PublicClientApplication`` does),
  not a token with application permissions for an app.
  """
- __instance, _tenant = None, "managed_identity" # Placeholders
+ __instance = "localhost" # We used to get this value from socket.getfqdn()
+ # but it is unreliable because getfqdn() either hangs or returns empty value
+ # on some misconfigured machines
+ _tenant = "managed_identity"
  _TOKEN_SOURCE = "token_source"
  _TOKEN_SOURCE_IDP = "identity_provider"
  _TOKEN_SOURCE_CACHE = "cache"
@@ -252,11 +254,6 @@ def __init__(
  self._token_cache = token_cache or TokenCache()
  self._client_capabilities = client_capabilities
 
- def _get_instance(self):
- if self.__instance is None:
- self.__instance = socket.getfqdn() # Moved from class definition to here
- return self.__instance
-
  def acquire_token_for_client(
  self,
  *,
@@ -302,7 +299,7 @@ def acquire_token_for_client(
  target=[resource],
  query=dict(
  client_id=client_id_in_cache,
- environment=self._get_instance(),
+ environment=self.__instance,
  realm=self._tenant,
  home_account_id=None,
  ),
@@ -344,7 +341,7 @@ def acquire_token_for_client(
  client_id=client_id_in_cache,
  scope=[resource],
  token_endpoint="https://{}/{}".format(
- self._get_instance(), self._tenant),
+ self.__instance, self._tenant),
  response=result,
  params={},
  data={},

tests/test_mi.py

@@ -190,8 +190,12 @@ def test_happy_path_of_vm(self):
  headers={'Metadata': 'true'},
  )
 
- @patch("msal.managed_identity.socket.getfqdn", new=lambda: "MixedCaseHostName")
- def test_happy_path_of_windows_vm(self):
+ @patch.object(ManagedIdentityClient, "_ManagedIdentityClient__instance", "MixedCaseHostName")
+ def test_happy_path_of_theoretical_mixed_case_hostname(self):
+ """Historically, we used to get the host name from socket.getfqdn(),
+ which could return a mixed-case host name on Windows.
+ Although we no longer use getfqdn(), we still keep this test case to ensure we tolerate it.
+ """
  self.test_happy_path_of_vm()
 
  @patch.dict(os.environ, {"AZURE_POD_IDENTITY_AUTHORITY_HOST": "http://localhost:1234//"})