Bdtjtk

I am trying to write a middleware that calls the next middleware and then whatever the response body of that middleware is, it will be changed by my middleware.

This is what the Configuration() method in the Startup class looks like:

public void Configuration(IAppBuilder app)

{

    app.Use<OAuthAuthenticationFailCustomResponse>();

    app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());

}

This is the middleware written by me:

public class OAuthAuthenticationFailCustomResponse : OwinMiddleware

{

    public OAuthAuthenticationFailCustomResponse(OwinMiddleware next)

        : base(next)

    {

    }



    public async override Task Invoke(IOwinContext context)

    {

        var stream = context.Response.Body;



        using (var buffer = new MemoryStream())

        {

            context.Response.Body = buffer;



            await Next.Invoke(context);



            buffer.Seek(0, SeekOrigin.Begin);



            var byteArray = Encoding.ASCII.GetBytes("Hello World");

            context.Response.StatusCode = 200;

            context.Response.ContentLength = byteArray.Length;



            buffer.SetLength(0);

            buffer.Write(byteArray, 0, byteArray.Length);

            buffer.Seek(0, SeekOrigin.Begin);

            buffer.CopyTo(stream);

        }

    }

}

However, I still receive the response of the OAuthBearerAuthentication middleware after calling the API, which is:

{
"Message": "Authorization has been denied for this request." }

This is where I learnt to write the code that changes the response body;

The original stream was not put back into the context response body

public async override Task Invoke(IOwinContext context) {

    // hold a reference to what will be the outbound/processed response stream object 

    var stream = context.Response.Body;



    // create a stream that will be sent to the response stream before processing

    using (var buffer = new MemoryStream()) {

         // set the response stream to the buffer to hold the unaltered response

        context.Response.Body = buffer;



        // allow other middleware to respond

        await Next.Invoke(context);



        // we have the unaltered response, go to start

        buffer.Seek(0, SeekOrigin.Begin);



        // read the stream from the buffer

        var reader = new StreamReader(buffer);

        string responseBody = reader.ReadToEnd();



        //...decide what you want to do with the responseBody from other middleware



        //custom response

        var byteArray = Encoding.ASCII.GetBytes("Hello World");



        //write custom response to stream

        stream.Write(byteArray, 0, byteArray.Length);



        //reset the response body back to the original stream

        context.Response.Body = stream;

        context.Response.StatusCode = 200;

        context.Response.ContentLength = byteArray.Length;

    }

}