Add Readme usage

README.md

@@ -1,5 +1,85 @@
 
-# Contributing
+# Microsoft Authentication Extensions for Python
+
+The Microsoft Authentication Extensions for Python offers secure mechanisms for client applications to perform cross-platform token cache serialization and persistence. It gives additional support to the [Microsoft Authentication Library for Python (MSAL)](https://github.com/AzureAD/microsoft-authentication-library-for-python). 
+
+MSAL Python supports an in-memory cache by default and provides the [SerializableTokenCache](https://msal-python.readthedocs.io/en/latest/#msal.SerializableTokenCache) to perform cache serialization. You can read more about this in the MSAL Python [documentation](https://docs.microsoft.com/en-us/azure/active-directory/develop/msal-python-token-cache-serialization). Developers are required to implement their own cache persistance across multiple platforms and Microsoft Authentication Extensions makes this simpler.
+
+The supported platforms are Windows, Mac and Linux. 
+- Windows - [DPAPI](https://docs.microsoft.com/en-us/dotnet/standard/security/how-to-use-data-protection) is used for encryption.
+- MAC - The MAC KeyChain is used.
+- Linux - [LibSecret](https://wiki.gnome.org/Projects/Libsecret) is used for encryption.
+
+> Note: It is recommended to use this library for cache persistance support for Public client applications such as Desktop apps only. In web applications, this may lead to scale and performance issues. Web applications are recommended to persist the cache in session. Take a look at this [webapp sample](https://github.com/Azure-Samples/ms-identity-python-webapp).
+
+## Installation
+
+You can find Microsoft Authentication Extensions for Python on [Pypi](https://pypi.org/project/msal-extensions/).
+1. If you haven't already, [install and/or upgrade the pip](https://pip.pypa.io/en/stable/installing/)
+   of your Python environment to a recent version. We tested with pip 18.1.
+2. Run `pip install msal-extensions`.
+
+## Versions
+
+This library follows [Semantic Versioning](http://semver.org/).
+
+You can find the changes for each version under
+[Releases](https://github.com/AzureAD/microsoft-authentication-extensions-for-python/releases).
+
+## Usage
+
+The Microsoft Authentication Extensions library provides the `PersistedTokenCache` which accepts a platform-dependent persistence instance. This token cache can then be used to instantiate the `PublicClientApplication` in MSAL Python. 
+
+The token cache includes a file lock, and auto-reload behavior under the hood.
+
+
+
+Here is an example of this pattern for multiple platforms (taken from the complete [sample here](https://github.com/AzureAD/microsoft-authentication-extensions-for-python/blob/dev/sample/token_cache_sample.py)):
+
+```python
+def build_persistence(location, fallback_to_plaintext=False):
+    """Build a suitable persistence instance based your current OS"""
+    if sys.platform.startswith('win'):
+        return FilePersistenceWithDataProtection(location)
+    if sys.platform.startswith('darwin'):
+        return KeychainPersistence(location, "my_service_name", "my_account_name")
+    if sys.platform.startswith('linux'):
+        try:
+            return LibsecretPersistence(
+                location,
+                schema_name="my_schema_name",
+                attributes={"my_attr1": "foo", "my_attr2": "bar"},
+                )
+        except:  # pylint: disable=bare-except
+            if not fallback_to_plaintext:
+                raise
+            logging.exception("Encryption unavailable. Opting in to plain text.")
+    return FilePersistence(location)
+
+persistence = build_persistence("token_cache.bin")
+print("Is this persistence encrypted?", persistence.is_encrypted)
+
+cache = PersistedTokenCache(persistence)
+```
+Now you can use it in an MSAL application like this:
+```python
+app = msal.PublicClientApplication("my_client_id", token_cache=cache)
+```
+
+## Community Help and Support
+
+We leverage Stack Overflow to work with the community on supporting Azure Active Directory and its SDKs, including this one!
+We highly recommend you ask your questions on Stack Overflow (we're all on there!).
+Also browse existing issues to see if someone has had your question before.
+
+We recommend you use the "msal" tag so we can see it!
+Here is the latest Q&A on Stack Overflow for MSAL:
+[http://stackoverflow.com/questions/tagged/msal](http://stackoverflow.com/questions/tagged/msal)
+
+
+## Contributing
+
+All code is licensed under the MIT license and we triage actively on GitHub.
 
 This project welcomes contributions and suggestions.  Most contributions require you to agree to a
 Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us
@@ -9,6 +89,7 @@ When you submit a pull request, a CLA-bot will automatically determine whether y
 a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the instructions
 provided by the bot. You will only need to do this once across all repos using our CLA.
 
-This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/).
-For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or
-contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.
+
+## We value and adhere to the Microsoft Open Source Code of Conduct
+
+This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/). For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.