Change OpenAPI document name resolution to be case-insensitive

Author: sander1095

src/OpenApi/src/Extensions/OpenApiServiceCollectionExtensions.cs

@@ -57,13 +57,35 @@ public static IServiceCollection AddOpenApi(this IServiceCollection services, st
         ArgumentNullException.ThrowIfNull(services);
         ArgumentNullException.ThrowIfNull(configureOptions);
 
-        services.AddOpenApiCore(documentName);
-        services.Configure<OpenApiOptions>(documentName, options =>
+        // We need to store the document name in a case-insensitive manner
+        // to support case-insensitive document name resolution.
+        // Keyed Services are case-sensitive by default, which doesn't work well for document names in ASP.NET Core
+        // as routing in ASP.NET Core is case-insensitive by default.
+        var lowercasedDocumentName = documentName.ToLowerInvariant();
+
+        AddOpenApiCore(services, lowercasedDocumentName);
+        services.Configure<OpenApiOptions>(lowercasedDocumentName, options =>
         {
-            options.DocumentName = documentName;
+            options.DocumentName = lowercasedDocumentName;
             configureOptions(options);
         });
         return services;
+
+        // The reason this method is a local function is to prevent case-sensitive document names being passed into this method (from other methods) in the future.
+        static IServiceCollection AddOpenApiCore(IServiceCollection services, string documentName)
+        {
+            services.AddEndpointsApiExplorer();
+            services.AddKeyedSingleton<OpenApiSchemaService>(documentName);
+            services.AddKeyedSingleton<OpenApiSchemaStore>(documentName);
+            services.AddKeyedSingleton<OpenApiDocumentService>(documentName);
+            // Required for build-time generation
+            services.AddSingleton<IDocumentProvider, OpenApiDocumentProvider>();
+            // Required to resolve document names for build-time generation
+            services.AddSingleton(new NamedService<OpenApiDocumentService>(documentName));
+            // Required to support JSON serializations
+            services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<JsonOptions>, OpenApiSchemaJsonOptions>());
+            return services;
+        }
     }
 
     /// <summary>
@@ -99,19 +121,4 @@ public static IServiceCollection AddOpenApi(this IServiceCollection services, Ac
     /// </example>
     public static IServiceCollection AddOpenApi(this IServiceCollection services)
         => services.AddOpenApi(OpenApiConstants.DefaultDocumentName);
-
-    private static IServiceCollection AddOpenApiCore(this IServiceCollection services, string documentName)
-    {
-        services.AddEndpointsApiExplorer();
-        services.AddKeyedSingleton<OpenApiSchemaService>(documentName);
-        services.AddKeyedSingleton<OpenApiSchemaStore>(documentName);
-        services.AddKeyedSingleton<OpenApiDocumentService>(documentName);
-        // Required for build-time generation
-        services.AddSingleton<IDocumentProvider, OpenApiDocumentProvider>();
-        // Required to resolve document names for build-time generation
-        services.AddSingleton(new NamedService<OpenApiDocumentService>(documentName));
-        // Required to support JSON serializations
-        services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<JsonOptions>, OpenApiSchemaJsonOptions>());
-        return services;
-    }
 }