Prevent auth_token from being overwritten with None

Summary

Addresses https://gitlab.indiscale.com/caosdb/customers/f-fit/management/-/issues/82 / https://gitlab.com/linkahead/linkahead-pylib/-/issues/103
The auth_token is no longer overwritten with None in authentication/interface/on_response(), preventing the AuthTokenAuthenticator from becoming invalid when a request does not provide a new token in the "Set-Cookie" header.
Test MR is here.

Test Environment

Manual Testing

Check List for the Author

• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• Annotations in code (Gitlab comments)

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

src/linkahead/connection/mockup.py

@@ -75,7 +75,7 @@ class MockUpServerConnection(CaosDBServerConnection):
     just returns predefined responses which mimic the LinkAhead server."""
 
     def __init__(self):
-        self.resources = [self._login]
+        self.resources = [self._login, self._logout]
 
     def _login(self, method, path, headers, body):
         if method == "POST" and path == "login":
@@ -84,6 +84,12 @@ class MockUpServerConnection(CaosDBServerConnection):
                                            "mockup-auth-token"},
                                   body="")
 
+    def _logout(self, method, path, headers, body):
+        if method in ["DELETE", "GET"] and path == "logout":
+            return MockUpResponse(200,
+                                  headers={},
+                                  body="")
+
     def configure(self, **kwargs):
         """This configure method does nothing."""