Add support for tracking third parties

When tracking issues from multiple third-parties, it would be very helpful if JIRA could track which third-party each user belonged to. With this information there is a lot that could be done:

• provide security so that third-party users have more privileges on issues from their own company
• extend the search interface so that users can simply search all of their own issues
• similarly these users can now create useful filters such as 'my company's open issue'

Ideally this company/third-party information would be collected in a secure way so that it can be relied upon.

• require the user provide an email from the company's domain, and then verify it
• require an administrative user from each company so that they can add and remove users

I realize that some of this could be done as custom fields and workflows, but it would make sense to me for this to be a core part of the product. For example, on jira.atlassian.com, I'd love to be able to write filters such as "my company's unresolved issues". I also would really like to be able to edit issues created by my co-workers, and to remove ex-employees or reassign their issues to someone else.