fix for swagger ui with csp

Dfe.Academies.Academisation.WebApi/Program.cs

@@ -1,4 +1,5 @@
 using System.Reflection;
+using System.Text;
 using System.Text.Json;
 using Dfe.Academies.Academisation.Core.Utils;
 using Dfe.Academies.Academisation.Data;
@@ -36,9 +37,12 @@
 using FluentValidation;
 using MediatR;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Options;
+using NetEscapades.AspNetCore.SecurityHeaders;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Converters;
 using Newtonsoft.Json.Serialization;
+using Swashbuckle.AspNetCore.SwaggerUI;
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -147,6 +151,35 @@
 builder.Services.ConfigureOptions<SwaggerOptions>();
 builder.Services.AddAutoMapper(typeof(AutoMapperProfile));
 
+builder.Services.AddHttpContextAccessor();
+
+builder.Services
+	.AddOptions<SwaggerUIOptions>()
+	.Configure<IHttpContextAccessor>((swaggerUiOptions, httpContextAccessor) =>
+	{
+		// 2. Take a reference of the original Stream factory which reads from Swashbuckle's embedded resources
+		var originalIndexStreamFactory = swaggerUiOptions.IndexStream;
+
+		// 3. Override the Stream factory
+		swaggerUiOptions.IndexStream = () =>
+		{
+			// 4. Read the original index.html file
+			using var originalStream = originalIndexStreamFactory();
+			using var originalStreamReader = new StreamReader(originalStream);
+			var originalIndexHtmlContents = originalStreamReader.ReadToEnd();
+
+			// 5. Get the request-specific nonce generated by NetEscapades.AspNetCore.SecurityHeaders
+			var requestSpecificNonce = httpContextAccessor.HttpContext.GetNonce();
+
+			// 6. Replace inline `<script>` and `<style>` tags by adding a `nonce` attribute to them
+			var nonceEnabledIndexHtmlContents = originalIndexHtmlContents
+				.Replace("<script>", $"<script nonce=\"{requestSpecificNonce}\">", StringComparison.OrdinalIgnoreCase)
+				.Replace("<style>", $"<style nonce=\"{requestSpecificNonce}\">", StringComparison.OrdinalIgnoreCase);
+
+			// 7. Return a new Stream that contains our modified contents
+			return new MemoryStream(Encoding.UTF8.GetBytes(nonceEnabledIndexHtmlContents));
+		};
+	});
 
 
 builder.Services.AddMediatR(cfg => cfg.RegisterServicesFromAssemblies(typeof(CreateLoanCommandHandler).GetTypeInfo().Assembly));
@@ -202,6 +235,19 @@
 		.AddContentSecurityPolicy(builder =>
 		{
 			builder.AddDefaultSrc().None();
+
+			// Only allow loading resources from this app by default
+			builder.AddDefaultSrc().Self();
+
+			builder.AddStyleSrc()
+			   .Self()
+			   // Allow nonce-enabled <style> tags
+			   .WithNonce();
+
+			builder.AddScriptSrc()
+			   .Self()
+			   // Allow nonce-enabled <script> tags
+			   .WithNonce();
 		})
 		.AddPermissionsPolicy(builder =>
 		{