As a web hosted service have you considered something like YubiKeys in addition to system passwords for second factor authentication?
http://www.yubico.com/yubikey
I think this might be a nice feature. This would allow system developers to limit who can submit signals to only those holding the right physical keys.
Yubico provide lots of easy ways to integrate this:
http://www.yubico.com/web-api-clients
What do you think? Is this a feature other system developers would like to have?
