Windows Server 2012: allow access to RD Web Access from the internet

Hi all,

I've set up an RDS farm with Windows Server 2012. I've 3 session host and 1 RD Web Access. RemoteApp works fine from the internal network, but from the internet I cannot access the web page. Note that:

1) I've purchased a public certificate rdfarm.mycompany.com

2) from the internal network I do testing with an entry in the hosts file of my workstation pointing rdfarm.mycompany.com to internal IP

3) I've configured my firewall for NAT, I can do telnet on port 443 from the internt

4) I can access https://rdfarm.mycomany.com that display the standard IIS page but when I try https://rdfarm.mycompany.com/RDWeb I get error 404 page not found

5) I've form authentication enabled.

Please help