diff --git a/lib/api/helpers.rb b/lib/api/helpers.rb
index ce7b7b49..c0ba8747 100644
--- a/lib/api/helpers.rb
+++ b/lib/api/helpers.rb
@@ -21,5 +21,21 @@ module Gitlab
     def authenticate!
       error!({'message' => '401 Unauthorized'}, 401) unless current_user
     end
+
+    def authorize! action, subject
+      unless abilities.allowed?(current_user, action, subject)
+        error!({'message' => '403 Forbidden'}, 403)
+      end
+    end
+
+    private 
+
+    def abilities
+      @abilities ||= begin
+                       abilities = Six.new
+                       abilities << Ability
+                       abilities
+                     end
+    end
   end
 end
diff --git a/lib/api/issues.rb b/lib/api/issues.rb
index 68cb7e05..4cfa7500 100644
--- a/lib/api/issues.rb
+++ b/lib/api/issues.rb
@@ -79,6 +79,8 @@ module Gitlab
       #   PUT /projects/:id/issues/:issue_id
       put ":id/issues/:issue_id" do
         @issue = user_project.issues.find(params[:issue_id])
+        authorize! :modify_issue, @issue
+
         parameters = {
           title: (params[:title] || @issue.title),
           description: (params[:description] || @issue.description),
diff --git a/lib/api/milestones.rb b/lib/api/milestones.rb
index 29f5efa4..7c684667 100644
--- a/lib/api/milestones.rb
+++ b/lib/api/milestones.rb
@@ -61,6 +61,8 @@ module Gitlab
       # Example Request:
       #   PUT /projects/:id/milestones/:milestone_id
       put ":id/milestones/:milestone_id" do
+        authorize! :admin_milestone, user_project
+
         @milestone = user_project.milestones.find(params[:milestone_id])
         parameters = {
           title: (params[:title] || @milestone.title),
diff --git a/lib/api/projects.rb b/lib/api/projects.rb
index 7da83429..05b07e8d 100644
--- a/lib/api/projects.rb
+++ b/lib/api/projects.rb
@@ -74,6 +74,7 @@ module Gitlab
       # Example Request:
       #   POST /projects/:id/users
       post ":id/users" do
+        authorize! :admin_project, user_project
         user_project.add_users_ids_to_team(params[:user_ids].values, params[:project_access])
         nil
       end
@@ -87,6 +88,7 @@ module Gitlab
       # Example Request:
       #   PUT /projects/:id/add_users
       put ":id/users" do
+        authorize! :admin_project, user_project
         user_project.update_users_ids_to_role(params[:user_ids].values, params[:project_access])
         nil
       end
@@ -99,6 +101,7 @@ module Gitlab
       # Example Request:
       #   DELETE /projects/:id/users
       delete ":id/users" do
+        authorize! :admin_project, user_project
         user_project.delete_users_ids_from_team(params[:user_ids].values)
         nil
       end
@@ -186,6 +189,8 @@ module Gitlab
       #   PUT /projects/:id/snippets/:snippet_id
       put ":id/snippets/:snippet_id" do
         @snippet = user_project.snippets.find(params[:snippet_id])
+        authorize! :modify_snippet, @snippet
+
         parameters = {
           title: (params[:title] || @snippet.title),
           file_name: (params[:file_name] || @snippet.file_name),
@@ -209,6 +214,8 @@ module Gitlab
       #   DELETE /projects/:id/snippets/:snippet_id
       delete ":id/snippets/:snippet_id" do
         @snippet = user_project.snippets.find(params[:snippet_id])
+        authorize! :modify_snippet, @snippet
+
         @snippet.destroy
       end