Add method to authorize reading from prometheus proxy

app/controllers/clusters/base_controller.rb

@@ -31,6 +31,10 @@ class Clusters::BaseController < ApplicationController
     access_denied! unless can?(current_user, :create_cluster, clusterable)
   end
+  def authorize_read_prometheus!
+    access_denied! unless can?(current_user, :read_prometheus, clusterable)
+  end
+
   def clusterable
     raise NotImplementedError
   end

app/policies/clusters/instance_policy.rb

@@ -8,6 +8,7 @@ module Clusters
       enable :create_cluster
       enable :update_cluster
       enable :admin_cluster
+      enable :read_prometheus
     end
   end
 end