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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def AuthorizingClient( domain, auth, request_encoder, response_decoder, user_agent=None ):
 """Creates a Freshbooks client for a freshbooks domain, using an auth object. """

    
    http_transport = transport.HttpTransport(
        api_url(domain),
        build_headers(auth, user_agent)
    )
    
    return client.Client(
        request_encoder,
        http_transport,
        response_decoder
    )