<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def from_sas_token(cls, address, sas_token, eventhub=None, **kwargs):
 """Create an EventHubClient from an existing auth token or token generator. :param address: The Event Hub address URL :type address: str :param sas_token: A SAS token or function that returns a SAS token. If a function is supplied, it will be used to retrieve subsequent tokens in the case of token expiry. The function should take no arguments. :type sas_token: str or callable :param eventhub: The name of the EventHub, if not already included in the address URL. :type eventhub: str :param debug: Whether to output network trace logs to the logger. Default is `False`. :type debug: bool :param http_proxy: HTTP proxy settings. This must be a dictionary with the following keys: 'proxy_hostname' (str value) and 'proxy_port' (int value). Additionally the following keys may also be present: 'username', 'password'. :type http_proxy: dict[str, Any] :param auth_timeout: The time in seconds to wait for a token to be authorized by the service. The default value is 60 seconds. If set to 0, no timeout will be enforced from the client. :type auth_timeout: int """

        address = _build_uri(address, eventhub)
        return cls(address, sas_token=sas_token, **kwargs)