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Solve the following problem using Python, implementing the functions described below, one line at a time
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<USER_TASK:>
Description:
 def get_session(self, username, password, remote="127.0.0.1", proxy=None):
 """Create a session for a user. Attempts to create a user session on the Crowd server. Args: username: The account username. password: The account password. remote: The remote address of the user. This can be used to create multiple concurrent sessions for a user. The host you run this program on may need to be configured in Crowd as a trusted proxy for this to work. proxy: Value of X-Forwarded-For server header. Returns: dict: A dict mapping of user attributes if the application authentication was successful. See the Crowd documentation for the authoritative list of attributes. None: If authentication failed. """


        params = {
            "username": username,
            "password": password,
            "validation-factors": {
                "validationFactors": [
                    {"name": "remote_address", "value": remote, },
                ]
            }
        }

        if proxy:
            params["validation-factors"]["validationFactors"].append({"name": "X-Forwarded-For", "value": proxy, })

        response = self._post(self.rest_url + "/session",
                              data=json.dumps(params),
                              params={"expand": "user"})

        # If authentication failed for any reason return None
        if not response.ok:
            return None

        # Otherwise return the user object
        return response.json()