Thank you for sharing your experience with this problem!
The Authentication key is needed only when connecting a Graphisoft ID to an end user. If your Graphisoft ID already belongs to a company (which is the situation that you had here), then after signing in, License Manager Tool won't ask for the Authentication key, but will show you the licenses available to you to download from the pool.
I hope this answers your question. Please let me know if you have anything unclear!