http://steamcommunity.com/dev
I have said multiple times that the API here is to provide web sites a way to let users register with Steam accounts instead of usernames and passwords.
To help you understand, Google acts the same with Google Accounts. One Google account is used to log into G-mail and other Google services.
There are web sites which let you use a Google account to log in, instead of registering with a site username and password.
The Steam OpenID API
acts like a Google account: It not only lets you log into Google services (in this case, Steampowered.com and Steamcommunity.com), but you can use the Google account to register with other sites (in this case, some of the "other sites" using Steam's OpenID API are garrysmod.org anđ gmodtower.com).
So I hope this clarifies what I have been asserting: a Steam account is like a Google account.
But only game developers can implement Steam authentication from an OpenID or SteamID in their game, since only Badspot knows Blockland.exe's source code.
So, in short,
Passwordless Steam-based authentication for multiple Blockland servers at once is impossible right now.