Provides a special implementation of performService(), that open()'s an OutputStream as necessary to the appropriate
directory for logging, based on the headers in the message, then logs the message to there with a minimum of
translation.
Used to log into a server that requires authentication; carries username and password information in strings, and
checks them against "authenticationList" in the objectRegistry.
Login() -
Constructor for class ecologylab.services.authentication.messages.Login
Should not normally be used; only for XML translations.