Startup idea: Password sharing site?

Working with clients, subcontracting, considering backup support options--in most cases there are at least two parties who really need the possibility of full access to a site/app/server. E.g.: the client should always be able to get to their stuff if needed, even if they don't know what they're doing; the consultant/developer needs access; if the consultant/developer is unavailable, some backup person should be able to get full access in case of emergency. Often this state of affairs persists for months and the need for access may be intermittent.

It's very hard to manage all this well. If you've experienced it, you know just what I mean.

So what about a service where you can store all your login credentials on a per-project basis and grant users access to a project generally or on a time-restricted basis?

Key features: * Users IDed with client certs. * All crypt done on the client--server never sees your passwords ever. * All access logged, and access by your "backup support" (e.g.) could trigger an alert to other project users. * Optional daemon account to whom you can grant access. Runs every day and attempts logging-in (ssh, ftp, http basic at first, later app-specific support) to everything in the account. Alerts everyone if a credential no longer works.

Worth paying for? Stupid idea? Been done already? I value your feedback.