SharedTokenCacheCredential lazily loads the cache (Azure#12172)

Author: chlowell

sdk/identity/azure-identity/azure/identity/_credentials/shared_cache.py

@@ -55,6 +55,9 @@ def get_token(self, *scopes, **kwargs):  # pylint:disable=unused-argument
         if not scopes:
             raise ValueError("'get_token' requires at least one scope")
 
+        if not self._initialized:
+            self._initialize()
+
         if not self._client:
             raise CredentialUnavailableError(message="Shared token cache unavailable")
 

sdk/identity/azure-identity/azure/identity/_internal/shared_token_cache.py

@@ -3,6 +3,7 @@
 # Licensed under the MIT License.
 # ------------------------------------
 import abc
+import platform
 import time
 
 from msal import TokenCache
@@ -107,20 +108,26 @@ def __init__(self, username=None, **kwargs):  # pylint:disable=unused-argument
             self._tenant_id = kwargs.pop("tenant_id", None)
 
         self._cache = kwargs.pop("_cache", None)
-        if not self._cache:
-            allow_unencrypted = kwargs.pop("allow_unencrypted_cache", False)
+        self._client = None  # type: Optional[AadClientBase]
+        self._client_kwargs = kwargs
+        self._client_kwargs["tenant_id"] = authenticating_tenant
+        self._initialized = False
+
+    def _initialize(self):
+        if self._initialized:
+            return
+
+        if not self._cache and self.supported():
+            allow_unencrypted = self._client_kwargs.get("allow_unencrypted_cache", False)
             try:
                 self._cache = load_user_cache(allow_unencrypted)
             except Exception:  # pylint:disable=broad-except
                 pass
 
         if self._cache:
-            self._client = self._get_auth_client(
-                authority=self._authority, cache=self._cache, tenant_id=authenticating_tenant, **kwargs
-            )  # type: Optional[AadClientBase]
-        else:
-            # couldn't load the cache -> credential will be unavailable
-            self._client = None
+            self._client = self._get_auth_client(authority=self._authority, cache=self._cache, **self._client_kwargs)
+
+        self._initialized = True
 
     @abc.abstractmethod
     def _get_auth_client(self, **kwargs):
@@ -236,12 +243,4 @@ def supported():
 
         :rtype: bool
         """
-        try:
-            load_user_cache(allow_unencrypted=False)
-        except NotImplementedError:
-            return False
-        except ValueError:
-            # cache is supported but can't be encrypted
-            pass
-
-        return True
+        return platform.system() in {"Darwin", "Linux", "Windows"}

sdk/identity/azure-identity/azure/identity/aio/_credentials/shared_cache.py

@@ -63,6 +63,9 @@ async def get_token(self, *scopes: str, **kwargs: "Any") -> "AccessToken":  # py
         if not scopes:
             raise ValueError("'get_token' requires at least one scope")
 
+        if not self._initialized:
+            self._initialize()
+
         if not self._client:
             raise CredentialUnavailableError(message="Shared token cache unavailable")
 

sdk/identity/azure-identity/tests/test_shared_cache_credential.py

@@ -31,6 +31,11 @@
 from helpers import build_aad_response, build_id_token, mock_response, Request, validating_transport
 
 
+def test_supported():
+    """the cache is supported on Linux, macOS, Windows, so this should pass unless you're developing on e.g. FreeBSD"""
+    assert SharedTokenCacheCredential.supported()
+
+
 def test_no_scopes():
     """The credential should raise when get_token is called with no scopes"""
 
@@ -717,14 +722,34 @@ def test_access_token_caching():
     )
 
 
+def test_initialization():
+    """the credential should attempt to load the cache only once, when it's first needed"""
+
+    with patch("azure.identity._internal.persistent_cache._load_persistent_cache") as mock_cache_loader:
+        mock_cache_loader.side_effect = Exception("it didn't work")
+
+        credential = SharedTokenCacheCredential()
+        assert mock_cache_loader.call_count == 0
+
+        for _ in range(2):
+            with pytest.raises(CredentialUnavailableError):
+                credential.get_token("scope")
+            assert mock_cache_loader.call_count == 1
+
+
 def test_authentication_record_authenticating_tenant():
     """when given a record and 'tenant_id', the credential should authenticate in the latter"""
 
     expected_tenant_id = "tenant-id"
     record = AuthenticationRecord("not- " + expected_tenant_id, "...", "...", "...", "...")
 
     with patch.object(SharedTokenCacheCredential, "_get_auth_client") as get_auth_client:
-        SharedTokenCacheCredential(authentication_record=record, _cache=TokenCache(), tenant_id=expected_tenant_id)
+        credential = SharedTokenCacheCredential(
+            authentication_record=record, _cache=TokenCache(), tenant_id=expected_tenant_id
+        )
+        with pytest.raises(CredentialUnavailableError):
+            # this raises because the cache is empty
+            credential.get_token("scope")
 
     assert get_auth_client.call_count == 1
     _, kwargs = get_auth_client.call_args

sdk/identity/azure-identity/tests/test_shared_cache_credential_async.py

@@ -26,6 +26,11 @@
 from test_shared_cache_credential import get_account_event, populated_cache
 
 
+def test_supported():
+    """the cache is supported on Linux, macOS, Windows, so this should pass unless you're developing on e.g. FreeBSD"""
+    assert SharedTokenCacheCredential.supported()
+
+
 @pytest.mark.asyncio
 async def test_no_scopes():
     """The credential should raise when get_token is called with no scopes"""
@@ -37,39 +42,53 @@ async def test_no_scopes():
 
 @pytest.mark.asyncio
 async def test_close():
-    transport = AsyncMockTransport()
+    async def send(*_, **__):
+        return mock_response(json_payload=build_aad_response(access_token="**"))
+
+    transport = AsyncMockTransport(send=send)
     credential = SharedTokenCacheCredential(
         _cache=populated_cache(get_account_event("test@user", "uid", "utid")), transport=transport
     )
 
+    # the credential doesn't open a transport session before one is needed, so we send a request
+    await credential.get_token("scope")
+
     await credential.close()
 
     assert transport.__aexit__.call_count == 1
 
 
 @pytest.mark.asyncio
 async def test_context_manager():
-    transport = AsyncMockTransport()
+    async def send(*_, **__):
+        return mock_response(json_payload=build_aad_response(access_token="**"))
+
+    transport = AsyncMockTransport(send=send)
     credential = SharedTokenCacheCredential(
         _cache=populated_cache(get_account_event("test@user", "uid", "utid")), transport=transport
     )
 
+    # async with before initialization: credential should call aexit but not aenter
     async with credential:
-        assert transport.__aenter__.call_count == 1
+        await credential.get_token("scope")
 
-    assert transport.__aenter__.call_count == 1
+    assert transport.__aenter__.call_count == 0
     assert transport.__aexit__.call_count == 1
 
+    # async with after initialization: credential should call aenter and aexit
+    async with credential:
+        await credential.get_token("scope")
+        assert transport.__aenter__.call_count == 1
+    assert transport.__aexit__.call_count == 2
+
 
 @pytest.mark.asyncio
 async def test_context_manager_no_cache():
     """the credential shouldn't open/close sessions when instantiated in an environment with no cache"""
 
     transport = AsyncMockTransport()
 
-    with patch(
-        "azure.identity._internal.shared_token_cache.load_user_cache", Mock(side_effect=NotImplementedError)
-    ):
+    with patch("azure.identity._internal.shared_token_cache.load_user_cache", Mock(side_effect=NotImplementedError)):
         credential = SharedTokenCacheCredential(transport=transport)
 
     async with credential:
@@ -666,14 +685,20 @@ async def test_auth_record_multiple_accounts_for_username():
     assert token.token == expected_access_token
 
 
-def test_authentication_record_authenticating_tenant():
+@pytest.mark.asyncio
+async def test_authentication_record_authenticating_tenant():
     """when given a record and 'tenant_id', the credential should authenticate in the latter"""
 
     expected_tenant_id = "tenant-id"
     record = AuthenticationRecord("not- " + expected_tenant_id, "...", "...", "...", "...")
 
     with patch.object(SharedTokenCacheCredential, "_get_auth_client") as get_auth_client:
-        SharedTokenCacheCredential(authentication_record=record, _cache=TokenCache(), tenant_id=expected_tenant_id)
+        credential = SharedTokenCacheCredential(
+            authentication_record=record, _cache=TokenCache(), tenant_id=expected_tenant_id
+        )
+        with pytest.raises(CredentialUnavailableError):
+            # this raises because the cache is empty
+            await credential.get_token("scope")
 
     assert get_auth_client.call_count == 1
     _, kwargs = get_auth_client.call_args
@@ -713,3 +738,20 @@ async def test_allow_unencrypted_cache():
 
     msal_extensions_patch.stop()
     platform_patch.stop()
+
+
+@pytest.mark.asyncio
+async def test_initialization():
+    """the credential should attempt to load the cache only once, when it's first needed"""
+
+    with patch("azure.identity._internal.persistent_cache._load_persistent_cache") as mock_cache_loader:
+        mock_cache_loader.side_effect = Exception("it didn't work")
+
+        credential = SharedTokenCacheCredential()
+        assert mock_cache_loader.call_count == 0
+
+        for _ in range(2):
+            with pytest.raises(CredentialUnavailableError):
+                await credential.get_token("scope")
+            assert mock_cache_loader.call_count == 1
+