Is an action filter appropriate for this registration scenario?

Is an action filter appropriate for this registration scenario?

I have a WebAPI and windows 8 client. Client users login on the client
side against the Azure ACS and then send a authentication token to my
WebAPI.
I would like to register new users when they call the service for the
first time (if the authentication token is valid and they call the service
for the first time).
I was thinking about creating an action filter for my WebAPI that will
create an account is the call comes from a new user.
Is this an appropriate use for the filter or should I consider other
alternatives?