Add support for gating access to key on stored using user supplied password.

[rmhrisk]

We want to provide the option to provide a secret at sign time to authorize use, we should, in theory, be able to do this by:

1. Creating the users asymmetric key in memory session
2. Generate a symmetric key from a pin
3. Encrypt asymetric key using symmetric key
4. Put encrypted key in data object on token.

This is a bit lame but will meet their requirements.