Edit Access to Single Record via URL

Edit Access to Single Record via URL

I'm developing a system to allow public users to request meetings and to include an approval process. What I'd like to do is have some way to allow the application to be reviewed by a staff member and approved, rejected, or sent back for comment. Where I'm hitting a snag, though, is in figuring out how to programmatically allow edit access to a single record without requiring the user to log in. The workflow I'm envisioning is roughly:

1. User submits request
2. Staff member reviews request and sends back request for comment
3. User receives email with details of request and a link to update their request
4. User updates their proposal
5. Staff member gives final approval.

Any ideas on how to do this?