SSO and messages

* removes unused third party package from requirements.txt
* adds KonovaSSOClient as subclass of sso.Client for more control over login, e.g. which user data shall not be updated (found in konoa/sso/sso.py)
* adds Messenger class for communicating with SSO server (found in konova/utils/messenger.py)

konova/sso/sso.py

@@ -0,0 +1,43 @@
+"""
+Author: Michel Peltriaux
+Organization: Struktur- und Genehmigungsdirektion Nord, Rhineland-Palatinate, Germany
+Contact: michel.peltriaux@sgdnord.rlp.de
+Created on: 17.08.21
+
+"""
+from django.contrib.auth.models import User
+from simple_sso.sso_client.client import Client
+
+
+class KonovaSSOClient(Client):
+    """ Konova specialized derivate of general sso.Client.
+
+    Adds some custom behaviour for konova usage.
+
+    """
+    def build_user(self, user_data):
+        """ Creates a user or updates user data
+
+        Args:
+            user_data ():
+
+        Returns:
+
+        """
+        try:
+            user = User.objects.get(username=user_data['username'])
+            # Update user data, excluding some changes
+            skipable_attrs = {
+                "username",
+                "is_staff",
+                "is_superuser",
+            }
+            for _attr, _val in user_data.items():
+                if _attr in skipable_attrs:
+                    continue
+                setattr(user, _attr, _val)
+        except User.DoesNotExist:
+            user = User(**user_data)
+        user.set_unusable_password()
+        user.save()
+        return user