ASP.NET WCF Web API .NET 4 - Set up security for REST API

I need someone with experience of the WCF Web API to walk me through securing a REST API I am developing for one of my clients. The overall project is proof-of-concept at this stage, so am looking for something quick that will work. I am an experienced C# developer, but not too hot on ASP.NET and WCF security.

The REST API is currently a prototype. Calling clients can POST a simple object to a URL, and receive a 201 Created status plus URL.

What I need to do is somehow secure the service, ideally at a transport level, so that:
1. Only authenticated users can successfully POST new objects
2. We can retrieve the identity of the authenticated user to lookup other information about them

This is an internet-facing service, so cannot use Windows integrated security or other LAN approaches.

In my ideal world, the engagement would go as follows:
1. You consult with me over my options
2. I send you the project and you configure
3. We do a Skype call or similar, so that I can understand what you've done

This is basically a consulting/advisory gig, looking for someone who can do a quick turnaround; expecting to pay for 2-4 hours of expertise initially.