Collaborating with Clients

[Sharon Desize]

Using Confluence as a way to colloborate on projects and then Jira for our dev team.   I would like to be able to give access to just the one project in Confluence for each outside group we are working with to collaborate in Confluence with us.  I see the anonymous user but unless I'm not understanding it's use properly, it appears to be an open access which I don't want to provide.  

How are other's handling this? I'm looking for Confluence to be more like Basecamp where people can upload, see and share information and not just our internal team.