How to customize error message of OAuthAuthorizationServerProvider?

Question

We are using the OAuthAuthorizationServerProvider class to do authorization in our ASP.NET Web Api app.

If the provided username and password is invalid in GrantResourceOwnerCredentials, the call

context.SetError( "invalid_grant", "The user name or password is incorrect." );

Produces the following Json result:

{
    "error": "invalid_grant",
    "error_description": "The user name or password is incorrect."
}

Is there any way to customize this error result?
I would like to make it consistent with default error message format used in other parts of the API:

{
    "message": "Some error occurred."
}

Is this possible to achieve with the OAuthAuthorizationServerProvider?

Answer 1

1+ again for "user2325333" and "Dasun's" answer his solution, your answers are good but still there is an issue . The Josn Tag still return {error:""}, thus I replace the context.Response.Body with empty MemoryStream and here the work example

public static class ContextHelper
{
    public static void SetCustomError(this OAuthGrantResourceOwnerCredentialsContext context,string error, string errorMessage)
    {
        var json = new ResponseMessage
        { Data = errorMessage, Message = error, IsError = true }.ToJsonString();
        context.SetError(json);
        context.Response.Write(json);
        Invoke(context);
    }
    public static string ToJsonString(this object obj)
    {
        return JsonConvert.SerializeObject(obj);
    }
    static async Task Invoke(OAuthGrantResourceOwnerCredentialsContext context)
    {
        var owinResponseStream = new MemoryStream();
        var customResponseBody = new System.Net.Http.StringContent(JsonConvert.SerializeObject(new ResponseMessage()));
        var customResponseStream = await customResponseBody.ReadAsStreamAsync();
        await customResponseStream.CopyToAsync(owinResponseStream);
        context.Response.ContentType = "application/json";
        context.Response.ContentLength = customResponseStream.Length;
        context.Response.Body = owinResponseStream;
    }
}
public class ResponseMessage
{
    public bool IsError { get; set; }
    public string Data { get; set; }
    public string Message { get; set; }
}

for usage of this context

 public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
    {
        if (!context.Match.Passcode)
        {
            context.SetCustomError("invalid_grant", "Passcode is invalid.");
            return;
        }
    }

The Result will be as

Answer 2

This is how I did it.

string jsonString = "{\"message\": \"Some error occurred.\"}";

// This is just a work around to overcome an unknown internal bug. 
// In future releases of Owin, you may remove this.
context.SetError(new string(' ',jsonString.Length-12)); 

context.Response.StatusCode = 400;
context.Response.Write(jsonString);

Answer 3

+1 for Dasun's answer. Here is how I extended it a bit further.

public class ErrorMessage
{
    public ErrorMessage(string message)
    {
        Message = message;
    }

    public string Message { get; private set; }
}

public static class ContextHelper
{
    public static void SetCustomError(this OAuthGrantResourceOwnerCredentialsContext context, string errorMessage)
    {
        var json = new ErrorMessage(errorMessage).ToJsonString();

        context.SetError(json);
        context.Response.Write(json);
    }
}

The .ToJsonString() is another extension method that uses the Newtonsoft.Json library.

public static string ToJsonString(this object obj)
    {
        return JsonConvert.SerializeObject(obj);
    }

Usage:

context.SetCustomError("something went wrong");