s will allow you to answer questions like "Which marketing channels leads to users churning after a month?" or "What do users do on our website before signing up?"

    In a purely back-end implementation, this means whenever an anonymous user does something, you'll want to send a session ID ([Django](https://stackoverflow.com/questions/526179/in-django-how-can-i-find-out-the-request-session-sessionid-and-use-it-as-a-vari), [Flask](https://stackoverflow.com/questions/15156132/flask-login-how-to-get-session-id)) with the capture call. Then, when that users signs up, you want to do an alias call with the session ID and the newly created user ID.

    The same concept applies for when a user logs in.

    An `alias` call requires
    - `previous distinct id` the unique ID of the user before
    - `distinct id` the current unique id

    For example:
    ```python
    posthog.alias('anonymous session id', 'distinct id')
    ```
    Ú