api_access.rb

#!/usr/bin/ruby

require 'rubygems'
require 'chef'
require 'chef/node'
require 'chef/rest'

# A registration for your API access
api_user = "monkey"
# A password for the API access
api_pass = "pants"
# A validation token, if you use them
validation_token = nil
# The name of a node to look up - replace dots with _
node_name = "latte_local"

rest = Chef::REST.new(Chef::Config[:registration_url])

## Basically, all this tear up stuff should be replaced with
## two method calls when CHEF-66 gets closed.

# First, we're going to create a false registration for 
# API access
rest.register(api_user, api_pass, validation_token)

# Then we authenticate
rest.authenticate(api_user, api_pass)

# Now you can do whatever you want, assuming you are validated
node = rest.get_rest("nodes/#{node_name}")
node[:signal] = "noise"

# Save it
rest.put_rest("nodes/#{node_name}", node)