CODE EXAMPLE FOR CSHARP

Modify middleware response c# .net

/// <summary>
/// The middleware Invoke method.
/// </summary>
/// <param name="httpContext">The current <see cref="HttpContext"/>.</param>
/// <returns>A Task to support async calls.</returns>
public async Task Invoke(HttpContext httpContext)
{
    var originBody = httpContext.Response.Body;
    try
    {
        var memStream = new MemoryStream();
        httpContext.Response.Body = memStream;

        await _next(httpContext).ConfigureAwait(false);

        memStream.Position = 0;
        var responseBody = new StreamReader(memStream).ReadToEnd();

        //Custom logic to modify response
        responseBody = responseBody.Replace("hello", "hi", StringComparison.InvariantCultureIgnoreCase);

        var memoryStreamModified = new MemoryStream();
        var sw = new StreamWriter(memoryStreamModified);
        sw.Write(responseBody);
        sw.Flush();
        memoryStreamModified.Position = 0;

        await memoryStreamModified.CopyToAsync(originBody).ConfigureAwait(false);
    }
    finally
    {
        httpContext.Response.Body = originBody;
    }
}