I am trying to make join a Riak node to the cluster programmatic but I can't manage to do that. I have tried this operation through web and Riak_control but I have a 403 forbidden HTTP error code.
I there any other way to join a cluster programmatic ?
There is no out-of-the-box way of doing it. You have to wrap the console commands for building a cluster in a Web service to call them remotely (e.g. RESTful API).
You may also try the experimental Riak Explorer, see Explorer API endpoints, #3.