If you setup a proper SSO it will not ask the login as users will be identified already by the SSO.
For other options you will need to provide more info on your current OBIEE setup: detailed version, security setup, how you expect to deal with security if you want to remove it etc.
You're not mentioning any version or platform in your question, but I recommend you start by familiarizing yourself with the security documentation:
Especially this part:
Also, there's a blog post from the CEAL team: