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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 make_service_url(self):
 """ Make the service URL CAS will use to redirect the browser back to this service. """

        cas_service_url = self.authenticator.cas_service_url
        if cas_service_url is None:
            cas_service_url = self.request.protocol + "://" + self.request.host + self.request.uri
        return cas_service_url