Reading Form Data in ActionFilterAttribute

Question

I created an ActionFilterAttribute for my web api in order to authorize people. Getting accessToken by RequestUri is okay, however i want to send it in form data. While reading Request.Content in onActionExecuting method of ActionFilterAttribute, server always has an empty result. How can i solve this problem? The code is as like as below:

    public class RequireAuthorization : ActionFilterAttribute
{

    public override void OnActionExecuting(System.Web.Http.Controllers.HttpActionContext actionContext)
    {
        actionContext.Request.Content.ReadAsStringAsync().ContinueWith((t) =>
        {
            try
            {
                //query will result in empty string
                string query = t.Result;

                string UserID = HttpUtility.ParseQueryString(query).Get("UserID");
                string accessToken = HttpUtility.ParseQueryString(query).Get("AccessToken");

                UserRepository repository = new UserRepository();
                repository.IsTokenValid(Convert.ToInt32(UserID), accessToken);
            }
            catch (Exception ex)
            {
                var response = new HttpResponseMessage
                {
                    Content =
                        new StringContent("This token is not valid, please refresh token or obtain valid token!"),
                    StatusCode = HttpStatusCode.Unauthorized
                };

                throw new HttpResponseException(response);
            }
        });


        base.OnActionExecuting(actionContext);
    }
}

score 8 · Accepted Answer · answered Sep 23 '12 at 10:26

It's is because the HttpContent has been read by the formatter before ActionFilter. Web API only allows reading content once. So you are unable to read it again.

Here is a possible solution to you. First, make your action parameter as FormDataCollection:

    [RequireAuthorization]
    public HttpResponseMessage PostTodo(FormDataCollection formData)
    {
        Todo todo = formData.ReadAs<Todo>();
        // ...

Then, get it in ActionFilter by code:

    public override void OnActionExecuting(System.Web.Http.Controllers.HttpActionContext actionContext)
    {
        var formData = actionContext.ActionArguments["formData"] as FormDataCollection;
        if (formData != null)
        {
            var userID = formData.Get("UserID");
            var accessToken = formData.Get("AccessToken");
            // authorize
        }

        base.OnActionExecuting(actionContext);
    }

Reading Form Data in ActionFilterAttribute

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