Auth failed usually means a mistake in the user(worker) name. It has to exactly match the login name you use in the web page.
The .machinename is optional, if you use it, it shows its pretty name in the dashboard. If you omit it, the hash rate shows in a generated "auto" miner. It really doesn't mind if you use it or not, and the password can even be blank or the classic x, doesn't matter.
Again: the username has to match exactly any caps used to login in the Slushpool web page.
Because of the minimal withdrawal amount, I'm not sure its such a good idea to use this old miner with Slushpool. You should really go with
https://solo.ckpool.orgBTW: You don't manually create workers in Slush Pool, at least not in its current UI incarnation. the .machinename in the miner user(worker) name field will do that automatically for you.
Kano pool does have a solo mode, but, you have to make an account (old accounts don't work) and configure it for solo mining. Unlike ckpool, where you just use your bitcoin address as user(worker) name and mine without needing to set up a pool account. Also dust payments like what this machine could only make, might take ages (if ever) for getting out any satoshis, not sure if he ever implemented the non manual method of paying dust. Oh and if he feels like your asic is funny, it gets banned, so there is that. In addition, 4 blocks per year is already on the lost cause side of the equation, i think that pool will close sooner than later, a shame since i love pplns pools the most, but a low hashrate for pplns means game over, as we have seen here before.