Kyfast/report to directive (#557)

closes #512

## All PRs:

* [x] Has tests
* [x] Documentation updated

## Adding a new header (Reporting-Endpoints)
**Is the header supported by any user agent?*
 Yes - Chrome 116+, Edge 116+, Opera 102+ (via Reporting API)

**What does it do?**
Defines HTTP reporting endpoints for CSP violations and other
security/performance reports using the HTTP Reporting API

**What are the valid values?**
Comma-separated pairs of [name="url"] where url must be HTTPS (e.g.,
csp-violations="https://example.com/reports")

**Where does the specification live?** 
[MDN
Reporting-Endpoints](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Reporting-Endpoints)
and [MDN report-to
directive](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Security-Policy/report-to)

## Adding a new CSP directive (report-to)

**Is the directive supported by any user agent?** 
Yes - Chrome 69+, Edge 79+, Firefox 110+, Safari 15.1+

**What does it do?**
Specifies a named reporting endpoint (defined via Reporting-Endpoints
header) where CSP violations should be reported, replacing or
complementing report-uri

**What are the valid values?**
A single string endpoint name (e.g., report-to csp-violations), must
match a name defined in the Reporting-Endpoints header

---------

Co-authored-by: Kylie Stradley <kyfast@users.noreply.github.com>

Author: KyFaSt

README.md

@@ -88,9 +88,50 @@ SecureHeaders::Configuration.default do |config|
     img_src: %w(somewhereelse.com),
     report_uri: %w(https://report-uri.io/example-csp-report-only)
   })
+
+  # Optional: Use the modern report-to directive (with Reporting-Endpoints header)
+  config.csp = config.csp.merge({
+    report_to: "csp-endpoint"
+  })
+
+  # When using report-to, configure the reporting endpoints header
+  config.reporting_endpoints = {
+    "csp-endpoint": "https://report-uri.io/example-csp",
+    "csp-report-only": "https://report-uri.io/example-csp-report-only"
+  }
 end
 ```
 
+### CSP Reporting
+
+SecureHeaders supports both the legacy `report-uri` and the modern `report-to` directives for CSP violation reporting:
+
+#### report-uri (Legacy)
+The `report-uri` directive sends violations to a URL endpoint. It's widely supported but limited to POST requests with JSON payloads.
+
+```ruby
+config.csp = {
+  default_src: %w('self'),
+  report_uri: %w(https://example.com/csp-report)
+}
+```
+
+#### report-to (Modern)
+The `report-to` directive specifies a named reporting endpoint defined in the `Reporting-Endpoints` header. This enables more flexible reporting through the HTTP Reporting API standard.
+
+```ruby
+config.csp = {
+  default_src: %w('self'),
+  report_to: "csp-endpoint"
+}
+
+config.reporting_endpoints = {
+  "csp-endpoint": "https://example.com/reports"
+}
+```
+
+**Recommendation:** Use both `report-uri` and `report-to` for maximum compatibility while transitioning to the modern approach.
+
 ### Deprecated Configuration Values
 * `block_all_mixed_content` - this value is deprecated in favor of `upgrade_insecure_requests`. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/block-all-mixed-content for more information.
 

lib/secure_headers.rb

@@ -11,6 +11,7 @@
 require "secure_headers/headers/referrer_policy"
 require "secure_headers/headers/clear_site_data"
 require "secure_headers/headers/expect_certificate_transparency"
+require "secure_headers/headers/reporting_endpoints"
 require "secure_headers/middleware"
 require "secure_headers/railtie"
 require "secure_headers/view_helper"

lib/secure_headers/configuration.rb

@@ -175,6 +175,7 @@ def create_noop_config_block(config)
       csp: ContentSecurityPolicy,
       csp_report_only: ContentSecurityPolicy,
       cookies: Cookie,
+      reporting_endpoints: ReportingEndpoints,
     }.freeze
 
     CONFIG_ATTRIBUTES = CONFIG_ATTRIBUTES_TO_HEADER_CLASSES.keys.freeze
@@ -211,6 +212,7 @@ def initialize(&block)
       @x_permitted_cross_domain_policies = nil
       @x_xss_protection = nil
       @expect_certificate_transparency = nil
+      @reporting_endpoints = nil
 
       self.referrer_policy = OPT_OUT
       self.csp = ContentSecurityPolicyConfig.new(ContentSecurityPolicyConfig::DEFAULT)
@@ -236,6 +238,7 @@ def dup
       copy.clear_site_data = @clear_site_data
       copy.expect_certificate_transparency = @expect_certificate_transparency
       copy.referrer_policy = @referrer_policy
+      copy.reporting_endpoints = self.class.send(:deep_copy_if_hash, @reporting_endpoints)
       copy
     end
 

lib/secure_headers/headers/content_security_policy.rb

@@ -63,6 +63,8 @@ def build_value
           build_sandbox_list_directive(directive_name)
         when :media_type_list
           build_media_type_list_directive(directive_name)
+        when :report_to_endpoint
+          build_report_to_directive(directive_name)
         end
       end.compact.join("; ")
     end
@@ -100,6 +102,13 @@ def build_media_type_list_directive(directive)
       end
     end
 
+    def build_report_to_directive(directive)
+      return unless endpoint_name = @config.directive_value(directive)
+      if endpoint_name && endpoint_name.is_a?(String) && !endpoint_name.empty?
+        [symbol_to_hyphen_case(directive), endpoint_name].join(" ")
+      end
+    end
+
     # Private: builds a string that represents one directive in a minified form.
     #
     # directive_name - a symbol representing the various ALL_DIRECTIVES
@@ -200,11 +209,12 @@ def append_nonce(source_list, nonce)
     end
 
     # Private: return the list of directives,
-    # starting with default-src and ending with report-uri.
+    # starting with default-src and ending with reporting directives (alphabetically ordered).
     def directives
       [
         DEFAULT_SRC,
         BODY_DIRECTIVES,
+        REPORT_TO,
         REPORT_URI,
       ].flatten
     end

lib/secure_headers/headers/policy_management.rb

@@ -39,6 +39,7 @@ def self.included(base)
     SCRIPT_SRC = :script_src
     STYLE_SRC = :style_src
     REPORT_URI = :report_uri
+    REPORT_TO = :report_to
 
     DIRECTIVES_1_0 = [
       DEFAULT_SRC,
@@ -51,7 +52,8 @@ def self.included(base)
       SANDBOX,
       SCRIPT_SRC,
       STYLE_SRC,
-      REPORT_URI
+      REPORT_URI,
+      REPORT_TO
     ].freeze
 
     BASE_URI = :base_uri
@@ -110,9 +112,9 @@ def self.included(base)
 
     ALL_DIRECTIVES = (DIRECTIVES_1_0 + DIRECTIVES_2_0 + DIRECTIVES_3_0 + DIRECTIVES_EXPERIMENTAL).uniq.sort
 
-    # Think of default-src and report-uri as the beginning and end respectively,
+    # Think of default-src and report-uri/report-to as the beginning and end respectively,
     # everything else is in between.
-    BODY_DIRECTIVES = ALL_DIRECTIVES - [DEFAULT_SRC, REPORT_URI]
+    BODY_DIRECTIVES = ALL_DIRECTIVES - [DEFAULT_SRC, REPORT_URI, REPORT_TO]
 
     DIRECTIVE_VALUE_TYPES = {
       BASE_URI                  => :source_list,
@@ -129,10 +131,11 @@ def self.included(base)
       NAVIGATE_TO               => :source_list,
       OBJECT_SRC                => :source_list,
       PLUGIN_TYPES              => :media_type_list,
+      PREFETCH_SRC              => :source_list,
+      REPORT_TO                 => :report_to_endpoint,
+      REPORT_URI                => :source_list,
       REQUIRE_SRI_FOR           => :require_sri_for_list,
       REQUIRE_TRUSTED_TYPES_FOR => :require_trusted_types_for_list,
-      REPORT_URI                => :source_list,
-      PREFETCH_SRC              => :source_list,
       SANDBOX                   => :sandbox_list,
       SCRIPT_SRC                => :source_list,
       SCRIPT_SRC_ELEM           => :source_list,
@@ -158,6 +161,7 @@ def self.included(base)
       FORM_ACTION,
       FRAME_ANCESTORS,
       NAVIGATE_TO,
+      REPORT_TO,
       REPORT_URI,
     ]
 
@@ -344,6 +348,8 @@ def validate_directive!(directive, value)
           validate_require_sri_source_expression!(directive, value)
         when :require_trusted_types_for_list
           validate_require_trusted_types_for_source_expression!(directive, value)
+        when :report_to_endpoint
+          validate_report_to_endpoint_expression!(directive, value)
         else
           raise ContentSecurityPolicyConfigError.new("Unknown directive #{directive}")
         end
@@ -398,6 +404,18 @@ def validate_require_trusted_types_for_source_expression!(directive, require_tru
         end
       end
 
+      # Private: validates that a report-to endpoint expression:
+      # 1. is a string
+      # 2. is not empty
+      def validate_report_to_endpoint_expression!(directive, endpoint_name)
+        unless endpoint_name.is_a?(String)
+          raise ContentSecurityPolicyConfigError.new("#{directive} must be a string. Found #{endpoint_name.class} value")
+        end
+        if endpoint_name.empty?
+          raise ContentSecurityPolicyConfigError.new("#{directive} must not be empty")
+        end
+      end
+
       # Private: validates that a source expression:
       # 1. is an array of strings
       # 2. does not contain any deprecated, now invalid values (inline, eval, self, none)

lib/secure_headers/headers/reporting_endpoints.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+module SecureHeaders
+  class ReportingEndpointsConfigError < StandardError; end
+  class ReportingEndpoints
+    HEADER_NAME = "reporting-endpoints".freeze
+
+    class << self
+      # Public: generate a Reporting-Endpoints header.
+      #
+      # The config should be a Hash of endpoint names to URLs.
+      # Example: { "csp-endpoint" => "https://example.com/reports" }
+      #
+      # Returns nil if config is OPT_OUT or nil, or a header name and
+      # formatted header value based on the config.
+      def make_header(config = nil)
+        return if config.nil? || config == OPT_OUT
+        validate_config!(config)
+        [HEADER_NAME, format_endpoints(config)]
+      end
+
+      def validate_config!(config)
+        case config
+        when nil, OPT_OUT
+          # valid
+        when Hash
+          config.each_pair do |name, url|
+            unless name.is_a?(String) && !name.empty?
+              raise ReportingEndpointsConfigError.new("Endpoint name must be a non-empty string, got: #{name.inspect}")
+            end
+            unless url.is_a?(String) && !url.empty?
+              raise ReportingEndpointsConfigError.new("Endpoint URL must be a non-empty string, got: #{url.inspect}")
+            end
+            unless url.start_with?("https://")
+              raise ReportingEndpointsConfigError.new("Endpoint URLs must use https, got: #{url.inspect}")
+            end
+          end
+        else
+          raise TypeError.new("Must be a Hash of endpoint names to URLs. Found #{config.class}: #{config}")
+        end
+      end
+
+      private
+
+      def format_endpoints(config)
+        config.map do |name, url|
+          %{#{name}="#{url}"}
+        end.join(", ")
+      end
+    end
+  end
+end

spec/lib/secure_headers/headers/content_security_policy_spec.rb

@@ -218,6 +218,31 @@ module SecureHeaders
         csp = ContentSecurityPolicy.new({ trusted_types: %w(blahblahpolicy 'allow-duplicates') })
         expect(csp.value).to eq("trusted-types blahblahpolicy 'allow-duplicates'")
       end
+
+      it "supports report-to directive with endpoint name" do
+        csp = ContentSecurityPolicy.new({ default_src: %w('self'), report_to: "csp-endpoint" })
+        expect(csp.value).to eq("default-src 'self'; report-to csp-endpoint")
+      end
+
+      it "includes report-to before report-uri in alphabetical order" do
+        csp = ContentSecurityPolicy.new({ default_src: %w('self'), report_uri: %w(/csp_report), report_to: "csp-endpoint" })
+        expect(csp.value).to eq("default-src 'self'; report-to csp-endpoint; report-uri /csp_report")
+      end
+
+      it "does not add report-to if the endpoint name is empty" do
+        csp = ContentSecurityPolicy.new({ default_src: %w('self'), report_to: "" })
+        expect(csp.value).to eq("default-src 'self'")
+      end
+
+      it "does not add report-to if not provided" do
+        csp = ContentSecurityPolicy.new({ default_src: %w('self') })
+        expect(csp.value).not_to include("report-to")
+      end
+
+      it "supports report-to without report-uri" do
+        csp = ContentSecurityPolicy.new({ default_src: %w('self'), report_to: "reporting-endpoint-name" })
+        expect(csp.value).to eq("default-src 'self'; report-to reporting-endpoint-name")
+      end
     end
   end
 end

spec/lib/secure_headers/headers/policy_management_spec.rb

@@ -169,6 +169,30 @@ module SecureHeaders
           ContentSecurityPolicy.validate_config!(ContentSecurityPolicyReportOnlyConfig.new(default_opts.merge(report_only: true)))
         end.to_not raise_error
       end
+
+      it "requires report_to to be a string" do
+        expect do
+          ContentSecurityPolicy.validate_config!(ContentSecurityPolicyConfig.new(default_opts.merge(report_to: ["endpoint"])))
+        end.to raise_error(ContentSecurityPolicyConfigError)
+      end
+
+      it "rejects empty report_to endpoint names" do
+        expect do
+          ContentSecurityPolicy.validate_config!(ContentSecurityPolicyConfig.new(default_opts.merge(report_to: "")))
+        end.to raise_error(ContentSecurityPolicyConfigError)
+      end
+
+      it "accepts valid report_to endpoint names" do
+        expect do
+          ContentSecurityPolicy.validate_config!(ContentSecurityPolicyConfig.new(default_opts.merge(report_to: "csp-endpoint")))
+        end.to_not raise_error
+      end
+
+      it "accepts report_to with hyphens and underscores" do
+        expect do
+          ContentSecurityPolicy.validate_config!(ContentSecurityPolicyConfig.new(default_opts.merge(report_to: "csp-endpoint_name-123")))
+        end.to_not raise_error
+      end
     end
 
     describe "#combine_policies" do