Implementing HTTP Request Handler on ASP.NET Core Applications

http-request-header-handler-middleware.cs

public class HttpRequestHeaderHandlerMiddleware
{
  private readonly RequestDelegate _next;
  ...

  public HttpRequestHeaderHandlerMiddleware(RequestDelegate next, ...)
  {
    this._next = next;
    ...
  }

  public async Task Invoke(HttpContext context)
  {
    ...
    await this.ProcessRequestAsync(..., context).ConfigureAwait(false);
  }

  private async Task ProcessRequestAsync(..., HttpContext context)
  {
    var uri = BuildUri(url, context);

    using (var client = new HttpClient())
    {
      ...

      // Add custom headers.
      foreach (var header in headers)
      {
        client.DefaultRequestHeaders.Add(header.Key, header.Value);
      }

      var result = await client.GetAsync(uri).ConfigureAwait(false);

      context.Response.StatusCode = (int)result.StatusCode;
      if (result.Content.Headers.ContentType != null)
      {
        context.Response.ContentType = result.Content.Headers.ContentType.MediaType;
      }

      var response = await result.Content.ReadAsStringAsync().ConfigureAwait(false);
      await context.Response.WriteAsync(response, Encoding.UTF8).ConfigureAwait(false);
    }
  }
}