feat: add pipeline to match user with uid

This allow if the response send correct uid and there is a user
with username equal, this match that user with using that uid.

feat: add tests for the pipe safer associate

This add tests for the pipe method `safer_associate_username_by_uid`

feat: separate exceptions file

Due pr recomendations is better to separate responsabilities of each file.
Exception file for tpa module created.

refactor: use ddt to check staff ^ superuser tests

eox_nelp/third_party_auth/exceptions.py

@@ -0,0 +1,12 @@
+"""Custom NELP  authentication Exceptions
+"""
+
+
+class EoxNelpAuthException(ValueError):
+    """Auth process exception.
+    Inspired in https://github.com/eduNEXT/eox-tenant/blob/master/eox_tenant/pipeline.py#L6
+    """
+
+    def __init__(self, backend, *args, **kwargs):
+        self.backend = backend
+        super().__init__(*args, **kwargs)

eox_nelp/third_party_auth/pipeline.py

@@ -8,6 +8,8 @@
 from django.contrib.auth import logout
 from social_core.pipeline.social_auth import social_details as social_core_details
 
+from eox_nelp.third_party_auth.exceptions import EoxNelpAuthException
+
 
 def social_details(backend, details, response, *args, **kwargs):
     """This is an extension of `social_core.pipeline.social_auth.social_details` that allows
@@ -65,3 +67,36 @@ def close_mismatch_session(request, *args, user=None, **kwargs):  # pylint: disa
         logout(request)
 
     return {}
+
+
+def safer_associate_username_by_uid(  # pylint: disable=unused-argument
+    backend, details, response, *args, user=None, **kwargs,
+):
+    """Pipeline to retrieve user if possible matching uid with the username of a user.
+    The uid is based in the configuration of the saml with the field `attr_user_permanent_id`:
+    https://github.com/python-social-auth/social-core/blob/master/social_core/backends/saml.py#L49
+
+    This is using the idp and the uid inspired in:
+    https://github.com/python-social-auth/social-core/blob/master/social_core/backends/saml.py#L296C23-L297
+    Raises:
+        EoxNelpAuthException: If someone tries to have staff or superuser permission using tpa.
+
+    Returns:
+        dict: Dict with user if matches, if not return None.
+    """
+    if user:
+        return None
+
+    idp = backend.get_idp(response["idp_name"])
+    uid = idp.get_user_permanent_id(response["attributes"])
+    user_match = backend.strategy.storage.user.get_user(username=uid)
+
+    if not user_match:
+        return None
+    if user_match.is_staff or user_match.is_superuser:
+        raise EoxNelpAuthException(backend, "It is not allowed to auto associate staff or admin users")
+
+    return {
+        "user": user_match,
+        "is_new": False,
+    }

eox_nelp/third_party_auth/tests/test_pipeline.py

@@ -0,0 +1,93 @@
+""" Test file for third_party_auth pipeline functions."""
+from ddt import data, ddt
+from django.contrib.auth import get_user_model
+from django.test import TestCase
+from mock import Mock
+
+from eox_nelp.third_party_auth.exceptions import EoxNelpAuthException
+from eox_nelp.third_party_auth.pipeline import safer_associate_username_by_uid
+
+User = get_user_model()
+
+
+@ddt
+class SaferAssociaciateUsernameUidTestCase(TestCase):
+    """Test class for safer_associate_username_by_uid method"""
+
+    def setUp(self):  # pylint: disable=invalid-name
+        """
+        Set base variables and objects across experience test cases.
+        """
+        self.details = {}
+        self.response = {
+            "idp_name": "tpa-saml-sso",
+            "attributes": {},
+        }
+        self.user, _ = User.objects.get_or_create(username="vader")
+
+    def test_user_already_matched(self):
+        """Test the pipeline method is called with already matched user.
+        Expected behavior:
+            - Return None.
+        """
+        backend = Mock()
+
+        pipe_output = safer_associate_username_by_uid(backend, self.details, self.response, user=self.user)
+
+        self.assertEqual(None, pipe_output)
+
+    def test_user_not_associated(self):
+        """Test the pipeline method try to match with uid but there is not user with that username.
+        Expected behavior:
+            - Pipe Return None.
+            - Strategy storage get_user method is called with desired params.
+        """
+        test_uid = "1888222999"
+        backend = Mock()
+        backend.get_idp.return_value.get_user_permanent_id.return_value = test_uid
+        backend.strategy.storage.user.get_user.return_value = None
+
+        pipe_output = safer_associate_username_by_uid(backend, self.details, self.response)
+
+        self.assertEqual(None, pipe_output)
+        backend.strategy.storage.user.get_user.assert_called_with(username=test_uid)
+
+    @data(
+        {"is_staff": True, "username": "1222333444"},
+        {"is_superuser": True, "username": "1222333555"},
+    )
+    def test_staff_user_raise_exc(self, user_kwargs):
+        """Test the pipeline method try to match with uid, the user with matched username exists
+        but is staff or superuser.
+        Expected behavior:
+            - Raise EoxNelpAuthException exception
+            - Strategy storage get_user method is called with desired params.
+        """
+        test_uid = user_kwargs["username"]
+        past_user, _ = User.objects.get_or_create(**user_kwargs)
+        backend = Mock()
+        backend.get_idp.return_value.get_user_permanent_id.return_value = test_uid
+        backend.strategy.storage.user.get_user.return_value = past_user
+
+        self.assertRaises(EoxNelpAuthException, safer_associate_username_by_uid, backend, self.details, self.response)
+        backend.strategy.storage.user.get_user.assert_called_with(username=test_uid)
+
+    def test_user_associate_username_with_uid(self):
+        """Test the pipeline method try to match with uid, the user with matched username exists
+        and is returned.
+        Expected behavior:
+            - Strategy storage get_user method is called with desired params.
+            - The method return the desirect with `user` and `is_new` keys.
+        """
+        test_uid = "1777888999"
+        past_user, _ = User.objects.get_or_create(
+            username=test_uid,
+        )
+        backend = Mock()
+        backend.get_idp.return_value.get_user_permanent_id.return_value = test_uid
+        backend.strategy.storage.user.get_user.return_value = past_user
+
+        pipe_output = safer_associate_username_by_uid(backend, self.details, self.response)
+
+        self.assertEqual({"user": past_user, "is_new": False}, pipe_output)
+        backend.strategy.storage.user.get_user.assert_called_with(username=test_uid)