Change form-action Content-Security-Policy directive to be more restrictive (#26897)

app/controllers/concerns/web_app_controller_concern.rb

@@ -8,6 +8,16 @@ module WebAppControllerConcern
 
     before_action :redirect_unauthenticated_to_permalinks!
     before_action :set_app_body_class
+
+    content_security_policy do |p|
+      policy = ContentSecurityPolicy.new
+
+      if policy.sso_host.present?
+        p.form_action policy.sso_host
+      else
+        p.form_action :none
+      end
+    end
   end
 
   def skip_csrf_meta_tags?

app/lib/content_security_policy.rb

@@ -13,6 +13,22 @@ class ContentSecurityPolicy
     [assets_host, cdn_host_value, paperclip_root_url].compact
   end
 
+  def sso_host
+    return unless ENV['ONE_CLICK_SSO_LOGIN'] == 'true' && ENV['OMNIAUTH_ONLY'] == 'true' && Devise.omniauth_providers.length == 1
+
+    provider = Devise.omniauth_configs[Devise.omniauth_providers[0]]
+    @sso_host ||= begin
+      case provider.provider
+      when :cas
+        provider.cas_url
+      when :saml
+        provider.options[:idp_sso_target_url]
+      when :openid_connect
+        provider.options.dig(:client_options, :authorization_endpoint) || OpenIDConnect::Discovery::Provider::Config.discover!(provider.options[:issuer]).authorization_endpoint
+      end
+    end
+  end
+
   private
 
   def url_from_configured_asset_host

config/initializers/content_security_policy.rb

@@ -12,24 +12,6 @@ policy = ContentSecurityPolicy.new
 assets_host = policy.assets_host
 media_hosts = policy.media_hosts
 
-def sso_host
-  return unless ENV['ONE_CLICK_SSO_LOGIN'] == 'true'
-  return unless ENV['OMNIAUTH_ONLY'] == 'true'
-  return unless Devise.omniauth_providers.length == 1
-
-  provider = Devise.omniauth_configs[Devise.omniauth_providers[0]]
-  @sso_host ||= begin
-    case provider.provider
-    when :cas
-      provider.cas_url
-    when :saml
-      provider.options[:idp_sso_target_url]
-    when :openid_connect
-      provider.options.dig(:client_options, :authorization_endpoint) || OpenIDConnect::Discovery::Provider::Config.discover!(provider.options[:issuer]).authorization_endpoint
-    end
-  end
-end
-
 Rails.application.config.content_security_policy do |p|
   p.base_uri        :none
   p.default_src     :none
@@ -40,8 +22,8 @@ Rails.application.config.content_security_policy do |p|
   p.media_src       :self, :data, *media_hosts
   p.manifest_src    :self, assets_host
 
-  if sso_host.present?
-    p.form_action :self, sso_host
+  if policy.sso_host.present?
+    p.form_action :self, policy.sso_host
   else
     p.form_action :self
   end

spec/requests/content_security_policy_spec.rb

@@ -26,7 +26,7 @@ RSpec.describe 'Content-Security-Policy' do
       connect-src 'self' data: blob: https://cb6e6126.ngrok.io #{Rails.configuration.x.streaming_api_base_url}
       default-src 'none'
       font-src 'self' https://cb6e6126.ngrok.io
-      form-action 'self'
+      form-action 'none'
       frame-ancestors 'none'
       frame-src 'self' https:
       img-src 'self' data: blob: https://cb6e6126.ngrok.io