ASP.NET Core + Swashbuckle OpenAPI Extensions sample

Program.cs

using Microsoft.OpenApi.Any;
using Microsoft.OpenApi.Extensions;
using Microsoft.OpenApi.Models;
using Swashbuckle.AspNetCore.SwaggerGen;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1", new() {Title = builder.Environment.ApplicationName, Version = "v1"});

    c.DocumentFilter<GoogleOpenApiExtensions>();
    c.OperationFilter<SomeOtherOpenApiExtensions>();
    c.SchemaFilter<SomeOtherOpenApiExtensions>();

    // add more filters as needed
});

var app = builder.Build();

app.UseSwagger();
app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", $"{builder.Environment.ApplicationName} v1"));

app.MapGet("/", () => "Hello World!");

app.Run();

internal class GoogleOpenApiExtensions : IDocumentFilter
{
    public void Apply(OpenApiDocument swaggerDoc, DocumentFilterContext context)
    {
        swaggerDoc.AddExtension(
            "x-google-backend",
            new OpenApiObject
            {
                ["address"] = new OpenApiString("http://some.backend.url")
            });
    }
}

internal class SomeOtherOpenApiExtensions : IOperationFilter, ISchemaFilter, IParameterFilter, IRequestBodyFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        operation.AddExtension(
            "x-some-operation-extension",
            new OpenApiObject
            {
                ["random-operation-metadata-array"] = new OpenApiArray
                {
                    new OpenApiString("awesome-operation"),
                    new OpenApiInteger(9000)
                },
                ["some-boolean"] = new OpenApiBoolean(true)
            });
    }

    public void Apply(OpenApiSchema schema, SchemaFilterContext context)
    {
        schema.AddExtension("x-some-schema-extension", new OpenApiString("hello!"));
    }

    public void Apply(OpenApiParameter parameter, ParameterFilterContext context)
    {
        // parameter.AddExtension ...
    }

    public void Apply(OpenApiRequestBody requestBody, RequestBodyFilterContext context)
    {
        // requestBody.AddExtension ...
    }
}