docs: Update README with module description and features

docs/README.rst

@@ -3,5 +3,33 @@
 Software Heritage - Authentication
 ==================================
 
-Authentication library for SWH (keycloak common utilities)
+``swh-auth`` is a set of utility libraries related to user authentication
+in applications and services based on the use of `Keycloak`_ and `OpenID Connect`_.
 
+`Keycloak`_ is an open source software enabling single sign-on (SSO) with identity
+and access management.
+
+`OpenID Connect`_ (OIDC) is an authentication layer on top of `OAuth 2.0`_, widely
+used in modern web applications and services.
+
+``swh-auth`` notably offers the following features:
+
+- the ``swh.auth.keycloak.KeycloakOpenIDConnect`` class to ease the
+  interaction with a Keycloak server
+
+- a ``pytest`` plugin with the ``keycloak_oidc`` fixture to mock Keycloak
+  responses in unit tests
+
+- generic backends, views and middlewares to easily plug OpenID Connect authentication
+  in any `Django`_ or `Django REST framework`_ application
+
+
+.. _Keycloak: https://www.keycloak.org/
+
+.. _OpenID Connect: https://openid.net/connect/
+
+.. _OAuth 2.0: https://oauth.net/2/
+
+.. _Django: https://www.djangoproject.com/
+
+.. _Django REST framework: https://www.django-rest-framework.org/
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