Unable to use setHeader on REST request.

I am trying to set some headers on a REST request and looking at the documentation it says that I can use the setHeader method to this. However when I run the workflow with this option set I get the following error.

Property or method 'setHeader' not found on object RESTRequest

Here is the code i am using

var PostResponse = BRHost.createRequest("POST", "/api/sessionMngr/?v=v1_1", null).execute();
var newPost = BRHost.createRequest("POST","/api/tenants");
newPost.contextType = "text/xml";
newPost.setHeader = ("Accept", "application/xml");
newPost.setHeader = ("Name", username);
etc...

I am running version 1.0.6.2501990 of the rest plugin, if that makes a difference.