Web API 以 XML 形式返回 OAuth 令牌

使用具有单个用户帐户的默认 Visual Studio 2013 Web API 项目模板，并使用 application/xml 的 Accept 标头发布到 /token 端点，服务器仍然以 JSON 形式返回响应：

{"access_token":"...","token_type":"bearer","expires_in":1209599}

有没有办法以 XML 形式获取令牌？

根据RFC6749响应格式应为 JSON，并且 Microsoft 相应地实现了它。我发现 JSON 格式是在Microsoft.Owin.Security.OAuth.OAuthAuthorizationServerHandler没有扩展手段的内部类。

我还遇到了需要在 XML 中进行令牌响应的情况。 我想出的最佳解决方案是在 Accept 标头中声明时实现 HttpModule 将 JSON 转换为 XML。

public class OAuthTokenXmlResponseHttpModule : IHttpModule
{
    private static readonly string FilterKey = typeof(OAuthTokenXmlResponseHttpModule).Name + typeof(MemoryStreamFilter).Name;

    public void Init(HttpApplication application)
    {
        application.BeginRequest += ApplicationOnBeginRequest;
        application.EndRequest += ApplicationOnEndRequest;
    }

    private static void ApplicationOnBeginRequest(object sender, EventArgs eventArgs)
    {
        var application = (HttpApplication)sender;

        if (ShouldConvertToXml(application.Context.Request) == false) return;

        var filter = new MemoryStreamFilter(application.Response.Filter);
        application.Response.Filter = filter;
        application.Context.Items[FilterKey] = filter;
    }

    private static bool ShouldConvertToXml(HttpRequest request)
    {
        var isTokenPath = string.Equals("/token", request.Path, StringComparison.InvariantCultureIgnoreCase);
        var header = request.Headers["Accept"];

        return isTokenPath && (header == "text/xml" || header == "application/xml");
    }

    private static void ApplicationOnEndRequest(object sender, EventArgs eventArgs)
    {
        var context = ((HttpApplication) sender).Context;

        var filter = context.Items[FilterKey] as MemoryStreamFilter;
        if (filter == null) return;

        var jsonResponse = filter.ToString();
        var xDocument = JsonConvert.DeserializeXNode(jsonResponse, "oauth");
        var xmlResponse = xDocument.ToString(SaveOptions.DisableFormatting);

        WriteResponse(context.Response, xmlResponse);
    }

    private static void WriteResponse(HttpResponse response, string xmlResponse)
    {
        response.Clear();
        response.ContentType = "application/xml;charset=UTF-8";
        response.Write(xmlResponse);
    }

    public void Dispose()
    {
    }
}

public class MemoryStreamFilter : Stream
{
    private readonly Stream _stream;
    private readonly MemoryStream _memoryStream = new MemoryStream();

    public MemoryStreamFilter(Stream stream)
    {
        _stream = stream;
    }

    public override void Flush()
    {
        _stream.Flush();
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        return _stream.Read(buffer, offset, count);
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        _memoryStream.Write(buffer, offset, count);
        _stream.Write(buffer, offset, count);
    }

    public override string ToString()
    {
        return Encoding.UTF8.GetString(_memoryStream.ToArray());
    }

    #region Rest of the overrides
    public override bool CanRead
    {
        get { throw new NotImplementedException(); }
    }

    public override bool CanSeek
    {
        get { throw new NotImplementedException(); }
    }

    public override bool CanWrite
    {
        get { throw new NotImplementedException(); }
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        throw new NotImplementedException();
    }

    public override void SetLength(long value)
    {
        throw new NotImplementedException();
    }

    public override long Length
    {
        get { throw new NotImplementedException(); }
    }

    public override long Position
    {
        get
        {
            throw new NotImplementedException();
        }
        set
        {
            throw new NotImplementedException();
        }
    }
    #endregion
}