Shared credentials as extension to shared repositories concept

.I like the Shared Repository functionality - it solves one of the pains.

I would love to have similar functionality for credentials.

We have multiple repositories on BitBucket that I would actually like to be accessible from Bamboo.
Current solution that we have is set up a dedicated user, invite it to the repository, ask the guy who created the user what the private key/password is and create new repository.

It would be much easier and straightforward if I could just define those credentials globally and select them when configuring the repository.

The security implications would be basicly the same as for shared repository (ok, now I would be able to access any repository instead of just the ones defined as Shared)