Sessions are designed for advanced use cases, being most relevant when Framework is deployed behind a proxy.

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Session information in event handlers

You can access the session’s unique id, HTTP headers and cookies from event handlers via the session argument —similarly to how state and payload are accessed. The data made available here is captured in the HTTP request that initialised the session. The session argument will contain a dictionary with the following keys: id, cookies and headers. Values for the last two are themselves dictionaries. 
# The following will output a dictionary
# with the session's id, cookies and headers.
def session_inspector(session):
    print(repr(session))
This enables you to adapt the logic of an event to a number of factors, such as the authenticated user’s role, preferred language, etc.

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Session verifiers

You can use session verifiers to accept or deny a session based on headers or cookies, thus making sure that users without the right privileges don’t get access to the initial state or components. Session verifiers are functions decorated with wf.session_verifier and are run every time a user requests a session. A True value means that the session must be accepted, a False value means that the session must be rejected. 
import writer as wf

# Users without the header x-success will be denied the session

@wf.session_verifier
def check_headers(headers):
    if headers.get("x-success") is None:
        return False
    return True