def get_account_linking_access_token(handler_input):
    """Return the access token in the request.

    The method retrieves the user's ``accessToken`` from the input request.
    Once a user successfully enables a skill and links their Alexa
    account to the skill, the input request will have the user's
    access token. A `None` value is returned if there is no access token
    in the input request. More information on this can be found here :
    https://developer.amazon.com/docs/account-linking/add-account-linking-logic-custom-skill.html

    :param handler_input: The handler input instance that is generally
        passed in the sdk's request and exception components
    :type handler_input: ask_sdk_core.handler_input.HandlerInput
    :return: User account linked access token if available. None if not
        available
    :rtype: Optional[str]
    """
    return handler_input.request_envelope.context.system.user.access_token
