diff --git a/StrictDocOslcRm.sln b/StrictDocOslcRm.sln
new file mode 100644
index 0000000..a5dc498
--- /dev/null
+++ b/StrictDocOslcRm.sln
@@ -0,0 +1,9 @@
+<Solution>
+  <Configurations>
+    <Platform Name="Any CPU" />
+    <Platform Name="x64" />
+    <Platform Name="x86" />
+  </Configurations>
+  <Project Path="StrictDocOslcRm/StrictDocOslcRm.csproj" />
+  <Project Path="StrictDocOslcRm.Tests/StrictDocOslcRm.Tests.csproj" />
+</Solution>
diff --git a/src/StrictDocOslcRmServer/StrictDocOslcRm.Tests/SecurityHeadersTests.cs b/src/StrictDocOslcRmServer/StrictDocOslcRm.Tests/SecurityHeadersTests.cs
new file mode 100644
index 0000000..77d0aaa
--- /dev/null
+++ b/src/StrictDocOslcRmServer/StrictDocOslcRm.Tests/SecurityHeadersTests.cs
@@ -0,0 +1,106 @@
+using System.Net;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.Playwright;
+
+namespace StrictDocOslcRm.Tests;
+
+[ClassDataSource<WebApplicationFactory<Program>>(Shared = SharedType.PerAssembly)]
+public class SecurityHeadersTests(WebApplicationFactory<Program> factory)
+{
+    private readonly WebApplicationFactory<Program> _factory = factory;
+
+    [Test]
+    public async Task SecurityHeaders_ArePresent_OnEmbeddableResource()
+    {
+        // Use HttpClient for checking headers directly
+        var client = _factory.CreateClient();
+        // Since we don't have real data, root might 404 but middleware still runs.
+        // Wait, root "/" maps to RequirementController.GetRequirementResource but requires query param 'a'.
+        // Without 'a', it returns 400 Bad Request. Middleware runs on 400 too.
+        var response = await client.GetAsync("/?a=123");
+
+        var headers = response.Headers;
+
+        // Assertions
+        await Assert.That(headers.Contains("X-Content-Type-Options")).IsTrue();
+        await Assert.That(headers.GetValues("X-Content-Type-Options").FirstOrDefault()).IsEqualTo("nosniff");
+
+        await Assert.That(headers.Contains("Referrer-Policy")).IsTrue();
+        await Assert.That(headers.GetValues("Referrer-Policy").FirstOrDefault()).IsEqualTo("strict-origin-when-cross-origin");
+
+        await Assert.That(headers.Contains("Permissions-Policy")).IsTrue();
+
+        // X-Frame-Options should be absent for embeddable
+        await Assert.That(headers.Contains("X-Frame-Options")).IsFalse();
+
+        // CSP should allow framing (frame-ancestors *)
+        await Assert.That(headers.Contains("Content-Security-Policy")).IsTrue();
+        var csp = headers.GetValues("Content-Security-Policy").FirstOrDefault();
+        await Assert.That(csp).IsNotNull();
+        await Assert.That(csp).Contains("frame-ancestors *");
+    }
+
+    [Test]
+    public async Task HstsHeader_IsPresent_InProduction()
+    {
+        var client = _factory
+            .WithWebHostBuilder(builder =>
+            {
+                builder.UseEnvironment("Production");
+            })
+            .CreateClient(new WebApplicationFactoryClientOptions
+            {
+                BaseAddress = new Uri("https://localhost")
+            });
+
+        var response = await client.GetAsync("/?a=123");
+        var headers = response.Headers;
+
+        // Verify Strict-Transport-Security
+        await Assert.That(headers.Contains("Strict-Transport-Security")).IsTrue();
+        var hsts = headers.GetValues("Strict-Transport-Security").FirstOrDefault();
+        await Assert.That(hsts).IsNotNull();
+        await Assert.That(hsts).Contains("max-age=");
+    }
+
+    [Test]
+    public async Task SecurityHeaders_ArePresent_OnSelector()
+    {
+        var client = _factory.CreateClient();
+        var response = await client.GetAsync("/oslc/service_provider/123/requirements/selector");
+
+        var headers = response.Headers;
+        // Even if 404 (document not found), the middleware checks PATH.
+        // However, if the controller returns 404, the response is generated.
+        // The middleware runs AFTER the controller (on the way back)? No, it wraps 'next'.
+        // So it adds headers to the response object.
+        // The middleware logic:
+        // await next(context);
+        // headers["..."] = ...
+        // So it adds headers AFTER the inner pipeline.
+
+        await Assert.That(headers.Contains("X-Frame-Options")).IsFalse();
+
+        var csp = headers.GetValues("Content-Security-Policy").FirstOrDefault();
+        await Assert.That(csp).IsNotNull();
+        await Assert.That(csp).Contains("frame-ancestors *");
+    }
+
+    [Test]
+    public async Task SecurityHeaders_ArePresent_OnNonEmbeddableResource()
+    {
+        var client = _factory.CreateClient();
+        // A route that is not whitelisted
+        var response = await client.GetAsync("/oslc/catalog/123");
+
+        var headers = response.Headers;
+
+        await Assert.That(headers.Contains("X-Frame-Options")).IsTrue();
+        await Assert.That(headers.GetValues("X-Frame-Options").FirstOrDefault()).IsEqualTo("DENY");
+
+        await Assert.That(headers.Contains("Content-Security-Policy")).IsTrue();
+        var csp = headers.GetValues("Content-Security-Policy").FirstOrDefault();
+        await Assert.That(csp).IsNotNull();
+        await Assert.That(csp).Contains("frame-ancestors 'none'");
+    }
+}
diff --git a/src/StrictDocOslcRmServer/StrictDocOslcRm.Tests/StrictDocOslcRm.Tests.csproj b/src/StrictDocOslcRmServer/StrictDocOslcRm.Tests/StrictDocOslcRm.Tests.csproj
index 971f365..ef3e30d 100644
--- a/src/StrictDocOslcRmServer/StrictDocOslcRm.Tests/StrictDocOslcRm.Tests.csproj
+++ b/src/StrictDocOslcRmServer/StrictDocOslcRm.Tests/StrictDocOslcRm.Tests.csproj
@@ -1,9 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>net10.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <OutputType>Exe</OutputType>
+    <PreserveCompilationContext>true</PreserveCompilationContext>
   </PropertyGroup>
 
   <ItemGroup>
@@ -12,6 +13,8 @@
 
   <ItemGroup>
     <PackageReference Include="dotNetRdf" Version="3.4.1" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="8.0.0" />
+    <PackageReference Include="Microsoft.Playwright" Version="1.57.0" />
     <PackageReference Include="NSubstitute" Version="5.3.0" />
     <PackageReference Include="OSLC4Net.Core" Version="0.6.3" />
     <PackageReference Include="OSLC4Net.Core.DotNetRdfProvider" Version="0.6.3" />
diff --git a/src/StrictDocOslcRmServer/StrictDocOslcRm/Middleware/SecurityHeadersMiddleware.cs b/src/StrictDocOslcRmServer/StrictDocOslcRm/Middleware/SecurityHeadersMiddleware.cs
new file mode 100644
index 0000000..1a6278c
--- /dev/null
+++ b/src/StrictDocOslcRmServer/StrictDocOslcRm/Middleware/SecurityHeadersMiddleware.cs
@@ -0,0 +1,76 @@
+using Microsoft.AspNetCore.Http;
+using System.Threading.Tasks;
+
+namespace StrictDocOslcRm.Middleware;
+
+public class SecurityHeadersMiddleware(RequestDelegate next)
+{
+    public async Task InvokeAsync(HttpContext context)
+    {
+        var headers = context.Response.Headers;
+
+        // X-Content-Type-Options
+        headers["X-Content-Type-Options"] = "nosniff";
+
+        // Referrer-Policy
+        headers["Referrer-Policy"] = "strict-origin-when-cross-origin";
+
+        // Permissions-Policy
+        headers["Permissions-Policy"] = "accelerometer=(), camera=(), geolocation=(), gyroscope=(), magnetometer=(), microphone=(), payment=(), usb=()";
+
+        // Determine if the endpoint should be embeddable
+        var path = context.Request.Path;
+        var isEmbeddable = IsEmbeddable(path);
+
+        if (isEmbeddable)
+        {
+            // Remove X-Frame-Options if present
+            headers.Remove("X-Frame-Options");
+        }
+        else
+        {
+            headers["X-Frame-Options"] = "DENY";
+        }
+
+        // Content-Security-Policy
+        var csp = BuildCsp(isEmbeddable);
+        headers["Content-Security-Policy"] = csp;
+
+        await next(context);
+    }
+
+    private static bool IsEmbeddable(PathString path)
+    {
+        if (!path.HasValue) return false;
+
+        var pathValue = path.Value!;
+
+        // RequirementController.GetRequirementResource -> /
+        if (pathValue == "/") return true;
+
+        // ServiceProviderController.RequirementSelector -> /oslc/service_provider/{documentMid}/requirements/selector
+        if (pathValue.StartsWith("/oslc/service_provider", StringComparison.OrdinalIgnoreCase) &&
+            pathValue.EndsWith("/requirements/selector", StringComparison.OrdinalIgnoreCase))
+        {
+            return true;
+        }
+
+        return false;
+    }
+
+    private static string BuildCsp(bool isEmbeddable)
+    {
+        var frameAncestors = isEmbeddable ? "*" : "'none'";
+
+        return "default-src 'self'; " +
+               "script-src 'self' 'unsafe-inline' https://unpkg.com; " +
+               "style-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net; " +
+               "font-src 'self' https://cdn.jsdelivr.net; " +
+               "img-src 'self' data:; " +
+               $"frame-ancestors {frameAncestors}; " +
+               "object-src 'none'; " +
+               "base-uri 'self'; " +
+               "form-action 'self'; " +
+               "upgrade-insecure-requests;";
+    }
+}
diff --git a/src/StrictDocOslcRmServer/StrictDocOslcRm/Program.cs b/src/StrictDocOslcRmServer/StrictDocOslcRm/Program.cs
index ea8d3b6..a783def 100644
--- a/src/StrictDocOslcRmServer/StrictDocOslcRm/Program.cs
+++ b/src/StrictDocOslcRmServer/StrictDocOslcRm/Program.cs
@@ -31,12 +31,21 @@
 // Register StrictDoc service
 builder.Services.AddSingleton<IStrictDocService, StrictDocService>();
 
+// Configure HSTS options
+builder.Services.AddHsts(options =>
+{
+    options.Preload = true;
+    options.IncludeSubDomains = true;
+    options.MaxAge = TimeSpan.FromDays(365);
+});
+
 var app = builder.Build();
 
 // Configure the HTTP request pipeline
 if (!app.Environment.IsDevelopment())
 {
     app.UseExceptionHandler("/error");
+    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
     app.UseHsts();
 }
 else
@@ -47,6 +56,9 @@
 //
 // app.UseHttpsRedirection();
 
+// Add security headers middleware
+app.UseMiddleware<SecurityHeadersMiddleware>();
+
 // Enable CORS
 app.UseCors();
 
@@ -61,3 +73,5 @@
 app.MapControllers();
 
 app.Run();
+
+public partial class Program { }
diff --git a/src/StrictDocOslcRmServer/StrictDocOslcRm/StrictDocOslcRm.csproj b/src/StrictDocOslcRmServer/StrictDocOslcRm/StrictDocOslcRm.csproj
index c6b793b..ce46820 100644
--- a/src/StrictDocOslcRmServer/StrictDocOslcRm/StrictDocOslcRm.csproj
+++ b/src/StrictDocOslcRmServer/StrictDocOslcRm/StrictDocOslcRm.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <TargetFramework>net10.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
   </PropertyGroup>