Update device create API

- Update the existing device if a device with existing unique_id is
   present

app/controllers/devices_controller.rb

@@ -1,9 +1,15 @@
 class DevicesController < ApplicationController
+  skip_before_filter :verify_authenticity_token
   respond_to :json
 
   def create
-    device = Device.create(device_params)
-    respond_with device, status: :created
+    device = Device.find_or_initialize_by(unique_id: device_params[:unique_id])
+    device.assign_attributes(device_params)
+    if device.save
+      render json: { access_token: device.access_token }, status: :created
+    else
+      render json: { error: device.errors.full_messages }, status: :unprocessable_entity
+    end
   end
 
   private