added @captainsafia's content

Author: bradygaster

src/quickstart/openapi.md

@@ -75,3 +75,63 @@ Using the default configuration, the Swagger UI test page is now available at `h
 ![Swagger UI](https://github.com/bradygaster/minimal-apis.github.io/blob/bradyg/openapi-doc/src/.vuepress/public/openapi/swagger-ui.png?raw=true)
 
 
+## Customizing OpenAPI
+
+Numerous extension methods exist to enable customization of the generated OpenAPI description. Endpoints defined via minimal APIs can be annotated with metadata for use in OpenAPI libraries with a series of extension methods.
+
+You can set the EndpointName or `EndpointGroupName` of an endpoint using the `WithName` and `WithGroupName` extension methods as follows.
+
+```csharp
+string SomeMessage() => "Hello World.";
+app.MapGet("/hello", SomeMessage).WithName("WelcomeMessage").WithGroupName("Greetings");
+```
+
+> Note: If you have multiple `WithName` statements on the same endpoint, the last endpoint will be favored.
+
+On the topic of endpoint names, by default, endpoints that use a method group or named lambda will have their endpoint name set to the method name. For example, in the code snippet below, the endpoint will have a default endpoint name of `SomeMessage`.
+
+```csharp
+string SomeMessage() => "Hello World.";
+app.MapGet("/hello", SomeMessage);
+```
+
+This default endpoint name can be overloaded by using the `WithName` extension method as referenced above.
+
+```csharp
+string SomeMessage() => "Hello World.";
+app.MapGet("/hello", SomeMessage).WithName("MyOwnSpecialName");
+```
+
+To omit an endpoint from being displayed in API metadata, you can use the ExcludeFromDescription extension method on the endpoint.
+
+```csharp
+string SomeMessage() => "Hello World.";
+app.MapGet("/hello", SomeMessage).ExcludeFromDescription();
+```
+
+Let's say that you did want an endpoint to be annotated. In addition to endpoint names, you can also use the various `ProducesX` endpoints to indicate the response types of a method. The available extension methods are:
+
+```csharp
+Produces<TResponse>(int statusCode = 200, 
+    string? contentType = "application/json", 
+    params string[] additionalContentTypes)
+
+Produces(int statusCode = 200, 
+    System.Type? responseType = null, 
+    string? contentType = "application/json", 
+    params string[] additionalContentTypes)
+
+ProducesProblem(int statusCode, 
+    string? contentType = "application/problem+json")
+
+ProducesValidationProblem(int statusCode = 400, 
+    string? contentType = "application/validationproblem+json")
+```
+
+In general, the `Produces` extension methods give you the flexibility to set a `ProblemDetails` response type for your endpoint or define what response it returns on happy-path scenarios. You can do this with the generic-typed implementation `Produces<TResponse>` or with the `Produces` attribute. So, for example, to define the response metadata for a POST method that returns a `Todo` or a `ProblemDetails` response you can annotate it using the following extension methods.
+
+```csharp
+app.MapPost("/todos", (Todo todo) => { ... })
+   .ProducesProblem(401)
+   .Produces<Todo>(201);
+```