Add doc for authN scenarios (Azure#500)

Author: justinyoo

README.md

@@ -16,6 +16,7 @@
   * [**Microsoft.Azure.Functions.Worker.Extensions.OpenApi**](docs/openapi-out-of-proc.md)
   * [**Microsoft.Azure.WebJobs.Extensions.OpenApi**](docs/openapi-in-proc.md)
   * [**Microsoft.Azure.WebJobs.Extensions.OpenApi.Core**](docs/openapi-core.md)
+* [**Securing Azure Functions Endpoints through OpenAPI Auth**](docs/openapi-auth.md): This document shows many various scenarios to add authN features including the built-in features and OAuth2 auth flows.
 * [**Azure Functions v1 Support**](docs/azure-functions-v1-support.md): This document shows how to support Azure Functions v1 runtime with this OpenAPI extension.
 * [**Integrating OpenAPI-enabled Azure Functions to Azure API Management**](docs/integrate-with-apim.md): This document shows how to integrate the Azure Functions application with [Azure API Management](https://docs.microsoft.com/azure/api-management/api-management-key-concepts?WT.mc_id=dotnet_0000_juyoo), via this OpenAPI extension.
 <!-- * [**Integrating OpenAPI-enabled Azure Functions to Power Platform**](docs/integrate-with-powerplatform.md): This document shows how to integrate the Azure Functions application with [Power Platform](https://powerplatform.microsoft.com/?WT.mc_id=dotnet_0000_juyoo), via this OpenAPI extension. -->

docs/images/securing-azure-function-endpoints-via-openapi-auth-01.png

@@ -324,8 +324,7 @@ if (!auth.IsNullOrDefault())
 }
 
 // Out-Of-Process Worker
-var auth = await this._context
-                        .SetApplicationAssemblyAsync(fi.Directory.FullName, appendBin: false)
+var auth = await context.SetApplicationAssemblyAsync(fi.Directory.FullName, appendBin: false)
                         .AuthorizeAsync(request)
                         .ConfigureAwait(false);
 if (!auth.IsNullOrDefault())
@@ -337,3 +336,5 @@ if (!auth.IsNullOrDefault())
     return response;
 }
 ```
+
+There are more authN scenarios described in this document, [Securing Azure Functions Endpoints through OpenAPI Auth](./openapi-auth.md). Take a look for more details.