diff --git a/.gitignore b/.gitignore
index 1b806a6..8bf087c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -334,3 +334,5 @@ ASALocalRun/
 .mfractor/
 
 .eggs/
+.env
+Session.vim
diff --git a/Dockerfile b/Dockerfile
index 8b506dd..1304b97 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,7 @@
 # TODO: Can this Dockerfile use multi-stage build?
+# https://testdriven.io/tips/6da2d9c9-8849-4386-b7f9-13b28514ded8/
 # Final size 690MB. (It would be 1.16 GB if started with python:3 as base)
-FROM python:3.12-slim
+FROM python:3.13-slim
 
 # Install Generic PyGObject (sans GTK)
 #The following somehow won't work:
@@ -9,7 +10,6 @@ RUN apt-get update && apt-get install -y \
   libcairo2-dev \
   libgirepository1.0-dev \
   python3-dev
-RUN pip install "pygobject>=3,<4"
 
 # Install MSAL Extensions dependencies
 # Don't know how to get container talk to dbus on host,
@@ -19,10 +19,10 @@ RUN apt-get install -y \
   gnome-keyring
 
 # Not strictly necessary, but we include a pytest (which is only 3MB) to facilitate testing.
-RUN pip install "pytest>=6,<7"
+RUN pip install "pygobject>=3,<4" "pytest>=6,<7"
 
 # Install MSAL Extensions. Upgrade the pinned version number to trigger a new image build.
-RUN pip install "msal-extensions==1.1"
+RUN pip install "msal-extensions==1.2"
 
 # This setup is inspired from https://github.com/jaraco/keyring#using-keyring-on-headless-linux-systems-in-a-docker-container
 ENTRYPOINT ["dbus-run-session", "--"]
diff --git a/docker_run.sh b/docker_run.sh
index 04914d7..c1ac96f 100755
--- a/docker_run.sh
+++ b/docker_run.sh
@@ -6,11 +6,10 @@ docker build -t $IMAGE_NAME - < Dockerfile
 echo "==== Integration Test for Persistence on Linux (libsecret) ===="
 echo "After seeing the bash prompt, run the following to test encryption on Linux:"
 echo "    pip install -e ."
-echo "    pytest -s tests/chosen_test_file.py"
-echo "Note that you probably need to set up ENV VAR for the test cases to run"
+echo "    pytest --capture=no -s tests/chosen_test_file.py"
+echo "Note: It will test portalocker-based lock when portalocker is installed, or test file-based lock otherwise."
 docker run --rm -it \
     --privileged \
-    --env-file .env \
     -w /home -v $PWD:/home \
     $IMAGE_NAME \
     $1
diff --git a/msal_extensions/__init__.py b/msal_extensions/__init__.py
index a9a7283..384f5fb 100644
--- a/msal_extensions/__init__.py
+++ b/msal_extensions/__init__.py
@@ -8,6 +8,5 @@
     KeychainPersistence,
     LibsecretPersistence,
     )
-from .cache_lock import CrossPlatLock
-from .token_cache import PersistedTokenCache
+from .token_cache import PersistedTokenCache, CrossPlatLock, LockError
 
diff --git a/msal_extensions/cache_lock.py b/msal_extensions/cache_lock.py
index 5f61413..e5ddf2b 100644
--- a/msal_extensions/cache_lock.py
+++ b/msal_extensions/cache_lock.py
@@ -5,12 +5,15 @@
 import time
 import logging
 
-import portalocker
+import portalocker  # pylint: disable=import-error
 
 
 logger = logging.getLogger(__name__)
 
 
+LockError = portalocker.exceptions.LockException
+
+
 class CrossPlatLock(object):
     """Offers a mechanism for waiting until another process is finished interacting with a shared
     resource. This is specifically written to interact with a class of the same name in the .NET
diff --git a/msal_extensions/filelock.py b/msal_extensions/filelock.py
new file mode 100644
index 0000000..2c02247
--- /dev/null
+++ b/msal_extensions/filelock.py
@@ -0,0 +1,62 @@
+"""A cross-process lock based on exclusive creation of a given file name"""
+import os
+import sys
+import errno
+import time
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+class LockError(RuntimeError):
+    """It will be raised when unable to obtain a lock"""
+
+
+class CrossPlatLock(object):
+    """This implementation relies only on ``open(..., 'x')``"""
+    def __init__(self, lockfile_path):
+        self._lockpath = lockfile_path
+
+    def __enter__(self):
+        self._create_lock_file('{} {}'.format(
+            os.getpid(),
+            sys.argv[0],
+            ).encode('utf-8'))  # pylint: disable=consider-using-f-string
+        return self
+
+    def _create_lock_file(self, content):
+        timeout = 5
+        check_interval = 0.25
+        current_time = getattr(time, "monotonic", time.time)
+        timeout_end = current_time() + timeout
+        while timeout_end > current_time():
+            try:
+                with open(self._lockpath, 'xb') as lock_file:  # pylint: disable=unspecified-encoding
+                    lock_file.write(content)
+                return None  # Happy path
+            except ValueError:  # This needs to be the first clause, for Python 2 to hit it
+                raise LockError("Python 2 does not support atomic creation of file")
+            except FileExistsError:  # Only Python 3 will reach this clause
+                logger.debug(
+                    "Process %d found existing lock file, will retry after %f second",
+                    os.getpid(), check_interval)
+                time.sleep(check_interval)
+        raise LockError(
+            "Unable to obtain lock, despite trying for {} second(s). "
+            "You may want to manually remove the stale lock file {}".format(
+                timeout,
+                self._lockpath,
+            ))
+
+    def __exit__(self, *args):
+        try:
+            os.remove(self._lockpath)
+        except OSError as ex:  # pylint: disable=invalid-name
+            if ex.errno in (errno.ENOENT, errno.EACCES):
+                # Probably another process has raced this one
+                # and ended up clearing or locking the file for itself.
+                logger.debug("Unable to remove lock file")
+            else:
+                raise
+
diff --git a/msal_extensions/libsecret.py b/msal_extensions/libsecret.py
index 5f81753..08c7028 100644
--- a/msal_extensions/libsecret.py
+++ b/msal_extensions/libsecret.py
@@ -40,9 +40,7 @@
 class LibSecretAgent(object):
     """A loader/saver built on top of low-level libsecret"""
     # Inspired by https://developer.gnome.org/libsecret/unstable/py-examples.html
-    def __init__(
-            # pylint: disable=too-many-arguments
-            # pylint: disable=too-many-positional-arguments
+    def __init__(  # pylint: disable=too-many-arguments,too-many-positional-arguments
             self,
             schema_name,
             attributes,  # {"name": "value", ...}
diff --git a/msal_extensions/token_cache.py b/msal_extensions/token_cache.py
index 93e8565..348424d 100644
--- a/msal_extensions/token_cache.py
+++ b/msal_extensions/token_cache.py
@@ -5,7 +5,13 @@
 
 import msal
 
-from .cache_lock import CrossPlatLock
+try:  # It needs portalocker
+    from .cache_lock import (  # pylint: disable=unused-import
+        CrossPlatLock,
+        LockError,  # We don't use LockError in this file, but __init__.py uses it.
+        )
+except ImportError:  # Falls back to file-based lock
+    from .filelock import CrossPlatLock, LockError  # pylint: disable=unused-import
 from .persistence import _mkdir_p, PersistenceNotFound
 
 
diff --git a/setup.py b/setup.py
index d16e5d8..6d43f08 100644
--- a/setup.py
+++ b/setup.py
@@ -20,10 +20,14 @@
     python_requires=">=3.7",
     install_requires=[
         'msal>=1.29,<2',  # Use TokenCache.search() from MSAL Python 1.29+
-        'portalocker<4,>=1.4',
 
         ## We choose to NOT define a hard dependency on this.
         # "pygobject>=3,<4;platform_system=='Linux'",
     ],
+    extras_require={
+        "portalocker": [
+            'portalocker<4,>=1.4',
+        ],
+    },
     tests_require=['pytest'],
 )
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cache_file_generator.py b/tests/cache_file_generator.py
index 4164314..377d2db 100644
--- a/tests/cache_file_generator.py
+++ b/tests/cache_file_generator.py
@@ -14,9 +14,10 @@
 import sys
 import time
 
-from portalocker import exceptions
+from msal_extensions import FilePersistence, CrossPlatLock, LockError
 
-from msal_extensions import FilePersistence, CrossPlatLock
+
+print("Testing with {}".format(CrossPlatLock))
 
 
 def _acquire_lock_and_write_to_cache(cache_location, sleep_interval):
@@ -31,7 +32,7 @@ def _acquire_lock_and_write_to_cache(cache_location, sleep_interval):
             time.sleep(sleep_interval)
             data += "> " + str(os.getpid()) + "\n"
             cache_accessor.save(data)
-    except exceptions.LockException as e:
+    except LockError as e:
         logging.warning("Unable to acquire lock %s", e)
 
 
diff --git a/tests/http_client.py b/tests/http_client.py
new file mode 100644
index 0000000..1cee3c5
--- /dev/null
+++ b/tests/http_client.py
@@ -0,0 +1,12 @@
+class MinimalResponse(object):  # Not for production use
+    def __init__(self, requests_resp=None, status_code=None, text=None, headers=None):
+        self.status_code = status_code or requests_resp.status_code
+        self.text = text if text is not None else requests_resp.text
+        self.headers = {} if headers is None else headers
+        self._raw_resp = requests_resp
+
+    def raise_for_status(self):
+        if self._raw_resp is not None:  # Turns out `if requests.response` won't work
+                                        # cause it would be True when 200<=status<400
+            self._raw_resp.raise_for_status()
+
diff --git a/tests/test_agnostic_backend.py b/tests/test_agnostic_backend.py
index 565de36..d241a2d 100644
--- a/tests/test_agnostic_backend.py
+++ b/tests/test_agnostic_backend.py
@@ -1,12 +1,15 @@
+import json
 import os
 import shutil
 import tempfile
+from unittest.mock import patch
 import sys
 
 import msal
 import pytest
 
 from msal_extensions import *
+from .http_client import MinimalResponse
 
 
 @pytest.fixture
@@ -16,18 +19,19 @@ def temp_location():
     shutil.rmtree(test_folder, ignore_errors=True)
 
 def _test_token_cache_roundtrip(persistence):
-    client_id = os.getenv('AZURE_CLIENT_ID')
-    client_secret = os.getenv('AZURE_CLIENT_SECRET')
-    if not (client_id and client_secret):
-        pytest.skip('no credentials present to test TokenCache round-trip with.')
-
     desired_scopes = ['https://graph.microsoft.com/.default']
     apps = [  # Multiple apps sharing same persistence
         msal.ConfidentialClientApplication(
-        client_id, client_credential=client_secret,
+        "fake_client_id", client_credential="fake_client_secret",
         token_cache=PersistedTokenCache(persistence)) for i in range(2)]
-    token1 = apps[0].acquire_token_for_client(scopes=desired_scopes)
-    assert token1["token_source"] == "identity_provider", "Initial token should come from IdP"
+    with patch.object(apps[0].http_client, "post", return_value=MinimalResponse(
+        status_code=200, text=json.dumps({
+            "token_type": "Bearer",
+            "access_token": "app token",
+            "expires_in": 3600,
+    }))) as mocked_post:
+        token1 = apps[0].acquire_token_for_client(scopes=desired_scopes)
+        assert token1["token_source"] == "identity_provider", "Initial token should come from IdP"
     token2 = apps[1].acquire_token_for_client(scopes=desired_scopes)  # Hit token cache in MSAL 1.23+
     assert token2["token_source"] == "cache", "App2 should hit cache written by app1"
     assert token1['access_token'] == token2['access_token'], "Cache should hit"
diff --git a/tests/test_cache_lock_file_perf.py b/tests/test_cache_lock_file_perf.py
index 8bc1a1c..a86bf82 100644
--- a/tests/test_cache_lock_file_perf.py
+++ b/tests/test_cache_lock_file_perf.py
@@ -5,7 +5,7 @@
 
 import pytest
 
-from cache_file_generator import _acquire_lock_and_write_to_cache
+from .cache_file_generator import _acquire_lock_and_write_to_cache
 
 
 @pytest.fixture
diff --git a/tests/test_crossplatlock.py b/tests/test_crossplatlock.py
index ea3c9d5..4aac516 100644
--- a/tests/test_crossplatlock.py
+++ b/tests/test_crossplatlock.py
@@ -1,5 +1,5 @@
 import pytest
-from msal_extensions.cache_lock import CrossPlatLock
+from msal_extensions import CrossPlatLock
 
 
 def test_ensure_file_deleted():
@@ -10,6 +10,7 @@ def test_ensure_file_deleted():
     except NameError:
         FileNotFoundError = IOError
 
+    print("Testing with {}".format(CrossPlatLock))
     with CrossPlatLock(lockfile):
         pass
 
diff --git a/tox.ini b/tox.ini
index 2f44068..93ef1c2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,7 +7,7 @@ passenv =
     GITHUB_ACTIONS
 
 commands =
-    pytest
+    {posargs:pytest --color=yes}
 
 [testenv:lint]
 deps =