Thanks for trying this out @neha!
With the "Quick Sign In" button, a throwaway key is generated on the fly and used to sign an auth response. It's just meant to demo the sign in process and isn't tied to long term account access. You'll still be able to access your Forum account via username and password.
And you can actually download the developer release here: https://github.com/blockstack/blockstack-portal/releases. Thanks for the feedback, we'll take a look at this page and see how we can improve it.