Feature/cross origin opener policy (#160)

* Added model for Cross-Origin-Opener-Policy

* Leveraged COOP models

* Added tests for COOP header

* Moved CORP model back to explicit constructor

* Added missing test for COOP in one-shot test

* Minor version bump

* Ran dotnet-format on codebase

* Checked off the COOP (Cross-Origin-Opener-Policy) header in list of supported headers

* Linked to docs files for some of the supported headers

* Moved detail about X-XSS-Protection header to a warning at the head of it's documentation

* Added docs page for Cross-Origin-Resource-Policy (CORP) header

* Altered order of Cache-Control header docs page

* Added docs page for the Cross-Origin-Opener-Policy (COOP) header

* Added links in index for CORP and COOP docs pages

---------

Co-authored-by: Jamie Taylor <jamie.taylor@rjj-software.co.uk>

docs/configuration/Cache-Control.md

@@ -1,6 +1,6 @@
 ---
 title: Cache-Control
-nav_order: 7
+nav_order: 8
 parent: Configuration
 layout: page
 ---

docs/configuration/Cross-Origin-Opener-Policy.md

@@ -0,0 +1,49 @@
+---
+title: Cross-Origin-Opener-Policy
+nav_order: 9
+parent: Configuration
+layout: page
+---
+
+The Mozilla Developer Network describes the Cross-Origin-Opener-Policy (COOP) header like this:
+
+{: .quote }
+> The HTTP Cross-Origin-Opener-Policy (COOP) response header allows a website to control whether a new top-level
+> document, opened using Window.open() or by navigating to a new page, is opened in the same browsing context group
+> (BCG) or in a new browsing context group.
+>
+> source: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Opener-Policy
+
+A COOP header can be added in one of two ways, either using the default middleware options:
+
+```csharp
+app.UseSecureHeadersMiddleware();
+```
+
+The above adds the COOP header with a `same-origin` value.
+
+Or by creating an instance of the `SecureHeadersMiddlewareBuilder` class using the following code:
+
+```csharp
+var customConfig = SecureHeadersMiddlewareBuilder
+    .CreateBuilder()
+    .UseCrossOriginOpenerPolicy()
+    .Build();
+
+app.UseSecureHeadersMiddleware(customConfig);
+```
+
+The above adds the COOP header with a `same-origin` value.
+
+## Full Options
+
+The COOP header object (known internally as `CrossOriginOpenerPolicy`) has the following options:
+
+- enum: `CrossOriginOpenerOptions`
+
+The values available for the `CrossOriginOpenerOptions` enum are:
+
+- `CrossOrigin`
+- `SameSite`
+- `SameOrigin`
+

docs/configuration/Cross-Origin-Resource-Policy.md

@@ -0,0 +1,47 @@
+---
+title: Cross-Origin-Resource-Policy
+nav_order: 7
+parent: Configuration
+layout: page
+---
+
+The Mozilla Developer Network describes the Cross-Origin-Resource-Policy (CORP) header like this:
+
+{: .quote }
+> The HTTP Cross-Origin-Resource-Policy response header indicates that the browser should block no-cors cross-origin or cross-site requests to the given resource.
+>
+> source: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Resource-Policy
+
+A CORP header can be added in one of two ways, either using the default middleware options:
+
+```csharp
+app.UseSecureHeadersMiddleware();
+```
+
+The above adds the CORP header with a `same-origin` value.
+
+Or by creating an instance of the `SecureHeadersMiddlewareBuilder` class using the following code:
+
+```csharp
+var customConfig = SecureHeadersMiddlewareBuilder
+    .CreateBuilder()
+    .UseCrossOriginResourcePolicy()
+    .Build();
+
+app.UseSecureHeadersMiddleware(customConfig);
+```
+
+The above adds the CORP header with a `same-origin` value.
+
+## Full Options
+
+The CORP header object (known internally as `CrossOriginResourcePolicy`) has the following options:
+
+- enum: `CrossOriginResourceOptions`
+
+The values available for the `CrossOriginResourceOptions` enum are:
+
+- `CrossOrigin`
+- `SameSite`
+- `SameOrigin`
+

docs/configuration/X-XSS-Protection.md

@@ -5,15 +5,16 @@ parent: Configuration
 layout: page
 ---
 
+{: .warning }
+Both the OWASP Secure Headers Project and MDN recommend not using this header with any value other than "0", which disabled the XSS Auditor. This is due to the X-XSS-Protection header having been dropped from most modern browsers and that using it (with a value other than "0") can cause additional security issues to present themselves. The recommended path forward is to use a [Content-Security-Policy (CSP)](Content-Security-Policy.md) header.
+
 The Mozilla Developer Network describes the X-XSS-Protection header like this:
 
 {: .quote }
 > The HTTP X-XSS-Protection response header was a feature of Internet Explorer, Chrome and Safari that stopped pages from loading when they detected reflected cross-site scripting (XSS) attacks. These protections are largely unnecessary in modern browsers when sites implement a strong Content-Security-Policy that disables the use of inline JavaScript ('unsafe-inline').
 >
 > source: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection
 
-Both the OWASP Secure Headers Project and MDN recommend not using this header with any value other than "0", which disabled the XSS Auditor. This is due to the X-XSS-Protection header having been dropped from most modern browsers and that using it (with a value other than "0") can cause additional security issues to present themselves. The recommended path forward is to use a [Content-Security-Policy (CSP)](Content-Security-Policy.md) header.
-
 As such, the only value that OwaspHeaders.Core supports for the X-XSS-Protection header is "0", and the header can be added in one of two ways:
 
 ```csharp

docs/index.md

@@ -78,16 +78,16 @@ This project is a work-in-progress, and headers will be added inline with Owasp
 
 The following list displays the status of all the current (as of Dec 27th, 2024) recommended headers:
 
-- [ ✅ ] Strict-Transport-Security 
-- [ ✅ ] X-Frame-Options
-- [ ✅ ] X-Content-Type-Options
+- [ ✅ ] [Strict-Transport-Security] 
+- [ ✅ ] [X-Frame-Options]
+- [ ✅ ] [X-Content-Type-Options]
 - [ ✅ ] Content-Security-Policy
-- [ ✅ ] X-Permitted-Cross-Domain-Policies 
-- [ ✅ ] Referrer-Policy
-- [ ✅ ] Cross-Origin-Resource-Policy 
-- [ ✅ ] Cache-Control
+- [ ✅ ] [X-Permitted-Cross-Domain-Policies] 
+- [ ✅ ] [Referrer-Policy]
+- [ ✅ ] [Cross-Origin-Resource-Policy]
+- [ ✅ ] [Cache-Control]
 - [ ❌ ] Clear-Site-Data
-- [ ❌ ] Cross-Origin-Opener-Policy
+- [ ✅ ] [Cross-Origin-Opener-Policy]
 - [ ❌ ] Cross-Origin-Embedder-Policy
 - [ ❌ ] Permissions-Policy
 
@@ -126,3 +126,11 @@ The `web.config` file will need to be copied to the server when the application
 [Configuration]: https://gaprogman.github.io/OwaspHeaders.Core/configuration/
 [this answer on ServerFault]: https://serverfault.com/a/1020784
 [OWASP Secure Headers List]: https://owasp.org/www-project-secure-headers/#div-headers
+[Strict-Transport-Security]: ./configuration/Strict-Transport-Security/
+[X-Frame-Options]: ./configuration/X-Frame-Options/
+[X-Content-Type-Options]: ./configuration/X-Content-Type-Options/
+[X-Permitted-Cross-Domain-Policies]: ./configuration/X-Permitted-Cross-Domain-Policies/
+[Referrer-Policy]: ./configuration/Referrer-Policy/
+[Cross-Origin-Resource-Policy]: ./configuration/Cross-Origin-Resource-Policy/
+[Cache-Control]: ./configuration/Cache-Control/
+[Cross-Origin-Opener-Policy]: ./configuration/Cross-Origin-Opener-Policy/

src/Constants.cs

@@ -26,4 +26,5 @@ public static class Constants
     public const string ExpectCtHeaderName = "Expect-CT";
 
     public const string CrossOriginResourcePolicyHeaderName = "Cross-Origin-Resource-Policy";
+    public const string CrossOriginOpenerPolicyHeaderName = "Cross-Origin-Opener-Policy";
 }

src/Extensions/SecureHeadersMiddlewareBuilder.cs

@@ -317,6 +317,29 @@ public static SecureHeadersMiddlewareConfiguration UseCrossOriginResourcePolicy(
         return config;
     }
 
+    /// <summary>
+    /// The HTTP Cross-Origin-Opener-Policy (COOP) response header allows a website to control
+    /// whether a new top-level document, opened using Window.open() or by navigating to a new
+    /// page, is opened in the same browsing context group (BCG) or in a new browsing context group.
+    /// Source: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Opener-Policy
+    /// </summary>
+    /// <param name="value">
+    /// The HTTP Cross-Origin-Opener-Policy response header value.
+    /// </param>
+    /// <remarks>
+    /// Defaults to "same-origin" (<see cref="CrossOriginOpenerPolicy.CrossOriginOpenerOptions.SameOrigin"/>)
+    /// which means that "Only requests from the same Origin (i.e. scheme + host + port) can read the resource."
+    ///</remarks>
+    public static SecureHeadersMiddlewareConfiguration UseCrossOriginOpenerPolicy(
+        this SecureHeadersMiddlewareConfiguration config,
+        CrossOriginOpenerPolicy.CrossOriginOpenerOptions value =
+            CrossOriginOpenerPolicy.CrossOriginOpenerOptions.SameOrigin)
+    {
+        config.UseCrossOriginOpenerPolicy = true;
+        config.CrossOriginOpenerPolicy = new CrossOriginOpenerPolicy(value);
+        return config;
+    }
+
     /// <summary>
     /// Used to set a list of URLs that the we want the middleware to NOT operate on
     /// </summary>

src/Extensions/SecureHeadersMiddlewareExtensions.cs

@@ -33,6 +33,7 @@ public static SecureHeadersMiddlewareConfiguration BuildDefaultConfiguration(
             .UseCacheControl()
             .UseXssProtection()
             .UseCrossOriginResourcePolicy()
+            .UseCrossOriginOpenerPolicy()
             .SetUrlsToIgnore(urlIgnoreList)
             .Build();
     }

src/Models/CrossOriginOpenerPolicy.cs

@@ -0,0 +1,88 @@
+namespace OwaspHeaders.Core.Models;
+
+/// <summary>
+/// Cross-Origin-Opener-Policy.
+/// The following text was taken from the OWASP Secure Headers Project:
+/// This response header (also named COOP) allows you to ensure a top-level
+/// document does not share a browsing context group with cross-origin documents.
+/// COOP will process-isolate your document and potential attackers can’t access
+/// to your global object if they were opening it in a popup, preventing a
+/// set of cross-origin attacks dubbed XS-Leaks (https://xsleaks.dev/)
+/// (source Mozilla MDN (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Opener-Policy)).
+
+
+/// </summary>
+public class CrossOriginOpenerPolicy : IConfigurationBase
+{
+    /// <summary>
+    /// Cross-Origin-Opener-Policy.
+    /// The following text was taken from the OWASP Secure Headers Project:
+    /// This response header (also named COOP) allows you to ensure a top-level
+    /// document does not share a browsing context group with cross-origin documents.
+    /// COOP will process-isolate your document and potential attackers can’t access
+    /// to your global object if they were opening it in a popup, preventing a
+    /// set of cross-origin attacks dubbed XS-Leaks (https://xsleaks.dev/)
+    /// (source Mozilla MDN (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Opener-Policy)).
+    /// </summary>
+    public CrossOriginOpenerPolicy(CrossOriginOpenerOptions value =
+        CrossOriginOpenerOptions.SameOrigin)
+    {
+        OptionValue = value;
+    }
+
+    /// <summary>
+    /// Allows the document to be added to its opener’s browsing context group
+    /// unless the opener itself has a COOP of same-origin or same-origin-allow-popups (it is the default value).
+    /// </summary>
+    private const string UnsafeNoneValue = "unsafe-none";
+
+    /// <summary>
+    /// Only requests from the same Site can read the resource.
+    /// </summary>
+    private const string SameOriginAllowPopupsValue = "same-origin-allow-popups";
+
+    /// <summary>
+    /// Retains references to newly opened windows or tabs which either
+    /// don’t set COOP or which opt out of isolation by setting a COOP
+    /// of unsafe-none
+    /// </summary>
+    public const string SameOriginValue = "same-origin";
+
+    public enum CrossOriginOpenerOptions
+    {
+        /// <summary>
+        /// <see cref="UnsafeNoneValue"/>
+        /// </summary>
+        UnsafeNone,
+
+        /// <summary>
+        /// <see cref="SameOriginAllowPopupsValue"/>
+        /// </summary>
+        SameOriginAllowPopups,
+
+        /// <summary>
+        /// <see cref="SameOriginValue"/>
+        /// </summary>
+        SameOrigin
+    };
+
+    private CrossOriginOpenerOptions OptionValue { get; }
+
+    /// <summary>
+    /// Builds the HTTP header value
+    /// </summary>
+    /// <returns>A string representing the HTTP header value</returns>
+    public string BuildHeaderValue()
+    {
+        switch (OptionValue)
+        {
+            case CrossOriginOpenerOptions.SameOriginAllowPopups:
+                return SameOriginAllowPopupsValue;
+            case CrossOriginOpenerOptions.UnsafeNone:
+                return UnsafeNoneValue;
+            case CrossOriginOpenerOptions.SameOrigin:
+            default:
+                return SameOriginValue;
+        }
+    }
+}