Accessing Session Using ASP.NET Web API

R

Rocklan

MVC

For an MVC project make the following changes (WebForms and Dot Net Core answer down below):

WebApiConfig.cs

public static class WebApiConfig
{
    public static string UrlPrefix         { get { return "api"; } }
    public static string UrlPrefixRelative { get { return "~/api"; } }

    public static void Register(HttpConfiguration config)
    {
        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: WebApiConfig.UrlPrefix + "/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }
}

Global.asax.cs

public class MvcApplication : System.Web.HttpApplication
{
    ...

    protected void Application_PostAuthorizeRequest()
    {
        if (IsWebApiRequest())
        {
            HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
        }
    }

    private bool IsWebApiRequest()
    {
        return HttpContext.Current.Request.AppRelativeCurrentExecutionFilePath.StartsWith(WebApiConfig.UrlPrefixRelative);
    }

}

This solution has the added bonus that we can fetch the base URL in javascript for making the AJAX calls:

_Layout.cshtml

<body>
    @RenderBody()

    <script type="text/javascript">
        var apiBaseUrl = '@Url.Content(ProjectNameSpace.WebApiConfig.UrlPrefixRelative)';
    </script>

    @RenderSection("scripts", required: false)

and then within our Javascript files/code we can make our webapi calls that can access the session:

$.getJSON(apiBaseUrl + '/MyApi')
   .done(function (data) {
       alert('session data received: ' + data.whatever);
   })
);

WebForms

Do the above but change the WebApiConfig.Register function to take a RouteCollection instead:

public static void Register(RouteCollection routes)
{
    routes.MapHttpRoute(
        name: "DefaultApi",
        routeTemplate: WebApiConfig.UrlPrefix + "/{controller}/{id}",
        defaults: new { id = RouteParameter.Optional }
    );
}

And then call the following in Application_Start:

WebApiConfig.Register(RouteTable.Routes);

Dot Net Core

Add the Microsoft.AspNetCore.Session NuGet package and then make the following code changes:

Startup.cs

Call the AddDistributedMemoryCache and AddSession methods on the services object within the ConfigureServices function:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();
    ...

    services.AddDistributedMemoryCache();
    services.AddSession();

and in the Configure function add a call to UseSession:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, 
ILoggerFactory loggerFactory)
{
    app.UseSession();
    app.UseMvc();

SessionController.cs

Within your controller, add a using statement at the top:

using Microsoft.AspNetCore.Http;

and then use the HttpContext.Session object within your code like so:

    [HttpGet("set/{data}")]
    public IActionResult setsession(string data)
    {
        HttpContext.Session.SetString("keyname", data);
        return Ok("session data set");
    }

    [HttpGet("get")]
    public IActionResult getsessiondata()
    {
        var sessionData = HttpContext.Session.GetString("keyname");
        return Ok(sessionData);
    }

you should now be able to hit:

http://localhost:1234/api/session/set/thisissomedata

and then going to this URL will pull it out:

http://localhost:1234/api/session/get

Plenty more info on accessing session data within dot net core here: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/app-state

Performance Concerns

Read Simon Weaver's answer below regarding performance. If you're accessing session data inside a WebApi project it can have very serious performance consequence - I have seen ASP.NET enforce a 200ms delay for concurrent requests. This could add up and become disastrous if you have many concurrent requests.

Security Concerns

Make sure you are locking down resources per user - an authenticated user shouldn't be able to retrieve data from your WebApi that they don't have access to.

Read Microsoft's article on Authentication and Authorization in ASP.NET Web API - https://www.asp.net/web-api/overview/security/authentication-and-authorization-in-aspnet-web-api

Read Microsoft's article on avoiding Cross-Site Request Forgery hack attacks. (In short, check out the AntiForgery.Validate method) - https://www.asp.net/web-api/overview/security/preventing-cross-site-request-forgery-csrf-attacks

Perfect. Simple and it works. For non-MVC, just add Application_PostAuthorizeRequest() to Global.ascx.cs.

Thanks @JCallico, I guess that most people hit the ASP.NET page first which creates the session.

I needed to modify IsWebApiRequest() to also return true where path starts with WebApiConfig.UrlPrefix, as well as WebApiConfig.UrlPrefixRelative. Other than that, works as expected.

One thing to mention regarding this fix. when setting the SessionStateBehavior to Required, you are bottlenecking the webapi, because all your requests will run syncronized due to locks on the session object. You could instead run it as SessionStateBehavior.Readonly. This way it will not create locks on the session object.

Be careful when setting the session state behavior to "Required". Requests with write permissions will lock the session and prevent multiple HttpApplications to be spawned per client. You should set the session state to an appropriate level for each route. Please refer to my answer here: stackoverflow.com/a/34727708/1412787

O

Owen Blacker

You can access session state using a custom RouteHandler.

// In global.asax
public class MvcApp : System.Web.HttpApplication
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        var route = routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
        route.RouteHandler = new MyHttpControllerRouteHandler();
    }
}

// Create two new classes
public class MyHttpControllerHandler
    : HttpControllerHandler, IRequiresSessionState
{
    public MyHttpControllerHandler(RouteData routeData) : base(routeData)
    { }
}
public class MyHttpControllerRouteHandler : HttpControllerRouteHandler
{
    protected override IHttpHandler GetHttpHandler(
        RequestContext requestContext)
    {
        return new MyHttpControllerHandler(requestContext.RouteData);
    }
}

// Now Session is visible in your Web API
public class ValuesController : ApiController
{
    public string Get(string input)
    {
        var session = HttpContext.Current.Session;
        if (session != null)
        {
            if (session["Time"] == null)
                session["Time"] = DateTime.Now;
            return "Session Time: " + session["Time"] + input;
        }
        return "Session is not availabe" + input;
    }
}

Found here: http://techhasnoboundary.blogspot.com/2012/03/mvc-4-web-api-access-session.html

Update: if your API functions read from session, and don't modify session, it might be a good idea to use IReadOnlySessionState instead of IRequiresSessionState. This ensures the session isn't locked during the processing of the API function.

not working for me in MVC 4 - route.RouteHandler is not even a property for me. @LachlanB seems to have what worked for me.

Thanks @bkwdesign for pointing out the MVC solution. This answer relates to Web API only.

This doesn't seem to support Route Attributes. Thoughts?

As bkwdesign pointed out, this is no longer supported. However, there is a way to define the session state behavior per route using DataTokens: stackoverflow.com/a/34727708/1412787

C

Community

Why to avoid using Session in WebAPI?

Performance, performance, performance!

There's a very good, and often overlooked reason why you shouldn't be using Session in WebAPI at all.

The way ASP.NET works when Session is in use is to serialize all requests received from a single client. Now I'm not talking about object serialization - but running them in the order received and waiting for each to complete before running the next. This is to avoid nasty thread / race conditions if two requests each try to access Session simultaneously.

Concurrent Requests and Session State Access to ASP.NET session state is exclusive per session, which means that if two different users make concurrent requests, access to each separate session is granted concurrently. However, if two concurrent requests are made for the same session (by using the same SessionID value), the first request gets exclusive access to the session information. The second request executes only after the first request is finished. (The second session can also get access if the exclusive lock on the information is freed because the first request exceeds the lock time-out.) If the EnableSessionState value in the @ Page directive is set to ReadOnly, a request for the read-only session information does not result in an exclusive lock on the session data. However, read-only requests for session data might still have to wait for a lock set by a read-write request for session data to clear.

So what does this mean for Web API? If you have an application running many AJAX requests then only ONE is going to be able to run at a time. If you have a slower request then it will block all others from that client until it is complete. In some applications this could lead to very noticeably sluggish performance.

So you should probably use an MVC controller if you absolutely need something from the users session and avoid the unncesessary performance penalty of enabling it for WebApi.

You can easily test this out for yourself by just putting Thread.Sleep(5000) in a WebAPI method and enable Session. Run 5 requests to it and they will take a total of 25 seconds to complete. Without Session they'll take a total of just over 5 seconds.

(This same reasoning applies to SignalR).

You can get around this by using [SessionState(SessionStateBehavior.ReadOnly)] if your method only reads from the session.

For your scenario of 5 concurrent requests, i am blocking the UI on the first request and not allowing them to create multiple requests until the last one ends. If i don't user session key, how will i authenticate the user if i am creating the web api for a mobile app?

A

Antony Scott

Well you're right, REST is stateless. If you use a session the processing will become stateful, subsequent requests will be able to use state (from a session).

In order for a session to be rehydrated, you'll need to supply a key to associate the state. In a normal asp.net application that key is supplied by using a cookie (cookie-sessions) or url parameter (cookieless sessions).

If you need a session forget rest, sessions are irrelevant in REST based designs. If you need a session for validation then use a token or authorise by IP addresses.

I'm not sure about this. In Microsoft's examples they show using the Authorize attribute. I've tried that and it works with Forms Based Authentication. The Web API is aware of the authentication state which is being passed in the default authentication cookie.

Here is the sample I'm referring to, code.msdn.microsoft.com/ASPNET-Web-API-JavaScript-d0d64dd7 . It uses the new REST based Web API implements Forms Authentication.

I've used the [Authorize] attribute successfully without needing session state. I just wrote an authentication message handler to set the identity.

Marked you down because you didn't offer an answer to his problem, and more so, the Web Api is an asynchronous framework that works great with an ajax heavy web app. No one said you had to respect all tenents of RESTful design to gain benefits from using the Web API framework.

@MarkS. is right to inform that Web API is not supposed to be aware of session state. Negative answer still remain an answer. Up vote.

S

Schiavini

Mark, if you check the nerddinner MVC example the logic is pretty much the same.

You only need to retrieve the cookie and set it in the current session.

Global.asax.cs

public override void Init()
{
    this.AuthenticateRequest += new EventHandler(WebApiApplication_AuthenticateRequest);
    base.Init();
}

void WebApiApplication_AuthenticateRequest(object sender, EventArgs e)
{
    HttpCookie cookie = HttpContext.Current.Request.Cookies[FormsAuthentication.FormsCookieName];
    FormsAuthenticationTicket ticket = FormsAuthentication.Decrypt(cookie.Value);

    SampleIdentity id = new SampleIdentity(ticket);
    GenericPrincipal prin = new GenericPrincipal(id, null); 

    HttpContext.Current.User = prin;
}

enter code here

You'll have to define your "SampleIdentity" class, which you can borrow from the nerddinner project.

The identity class is in NerdDinner_2.0\NerdDinner\Models\NerdIdentity.cs.

This doesn't work for me (in .NET 4). I never have that cookie. Does it only work if you have FormsAuthentication turned on?

the cookie does indeed get generated after you authenticate through the login form. You could also customise how/when it gets created, see stackoverflow.com/questions/7217105 But you still need the user to effectively authenticate against the web server

The question asks for HttpContext.Current.Session and this answer does not clearly explains what needs to be done. See @LachlanB answer.

n

nhahtdh

To fix the issue:

protected void Application_PostAuthorizeRequest()
{
    System.Web.HttpContext.Current.SetSessionStateBehavior(System.Web.SessionState.SessionStateBehavior.Required);
}

in Global.asax.cs

Warning! This will enable session for ALL requests. This can really hurt performance if your application is using embedded resources.

@cgatian any alternative solution fixed ?

I think the best approach is what @Treyphor suggests. Don't enable it for all requests. Just routes that have "/api" or something in the URL. Also, if possible set session state to read only for your API controllers.

C

Cruiser KID

Last one is not working now, take this one, it worked for me.

in WebApiConfig.cs at App_Start

    public static string _WebApiExecutionPath = "api";

    public static void Register(HttpConfiguration config)
    {
        var basicRouteTemplate = string.Format("{0}/{1}", _WebApiExecutionPath, "{controller}");

        // Controller Only
        // To handle routes like `/api/VTRouting`
        config.Routes.MapHttpRoute(
            name: "ControllerOnly",
            routeTemplate: basicRouteTemplate//"{0}/{controller}"
        );

        // Controller with ID
        // To handle routes like `/api/VTRouting/1`
        config.Routes.MapHttpRoute(
            name: "ControllerAndId",
            routeTemplate: string.Format ("{0}/{1}", basicRouteTemplate, "{id}"),
            defaults: null,
            constraints: new { id = @"^\d+$" } // Only integers 
        );

Global.asax

protected void Application_PostAuthorizeRequest()
{
  if (IsWebApiRequest())
  {
    HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
  }
}

private static bool IsWebApiRequest()
{
  return HttpContext.Current.Request.AppRelativeCurrentExecutionFilePath.StartsWith(_WebApiExecutionPath);
}

fournd here: http://forums.asp.net/t/1773026.aspx/1

This is the simplest solution but has a few mistakes in the code so that it doesn't actually work. I have posted another solution based on this one, feel free to edit yours to match mine.

Slight correction on the _WebApiExecutionPath line needs to read public static string _WebApiExecutionPath = "~/api";

S

Stumblor

Following on from LachlanB's answer, if your ApiController doesn't sit within a particular directory (like /api) you can instead test the request using RouteTable.Routes.GetRouteData, for example:

protected void Application_PostAuthorizeRequest()
    {
        // WebApi SessionState
        var routeData = RouteTable.Routes.GetRouteData(new HttpContextWrapper(HttpContext.Current));
        if (routeData != null && routeData.RouteHandler is HttpControllerRouteHandler)
            HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
    }

T

Treyphor

I had this same problem in asp.net mvc, I fixed it by putting this method in my base api controller that all my api controllers inherit from:

    /// <summary>
    /// Get the session from HttpContext.Current, if that is null try to get it from the Request properties.
    /// </summary>
    /// <returns></returns>
    protected HttpContextWrapper GetHttpContextWrapper()
    {
      HttpContextWrapper httpContextWrapper = null;
      if (HttpContext.Current != null)
      {
        httpContextWrapper = new HttpContextWrapper(HttpContext.Current);
      }
      else if (Request.Properties.ContainsKey("MS_HttpContext"))
      {
        httpContextWrapper = (HttpContextWrapper)Request.Properties["MS_HttpContext"];
      }
      return httpContextWrapper;
    }

Then in your api call that you want to access the session you just do:

HttpContextWrapper httpContextWrapper = GetHttpContextWrapper();
var someVariableFromSession = httpContextWrapper.Session["SomeSessionValue"];

I also have this in my Global.asax.cs file like other people have posted, not sure if you still need it using the method above, but here it is just in case:

/// <summary>
/// The following method makes Session available.
/// </summary>
protected void Application_PostAuthorizeRequest()
{
  if (HttpContext.Current.Request.AppRelativeCurrentExecutionFilePath.StartsWith("~/api"))
  {
    HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
  }
}

You could also just make a custom filter attribute that you can stick on your api calls that you need session, then you can use session in your api call like you normally would via HttpContext.Current.Session["SomeValue"]:

  /// <summary>
  /// Filter that gets session context from request if HttpContext.Current is null.
  /// </summary>
  public class RequireSessionAttribute : ActionFilterAttribute
  {
    /// <summary>
    /// Runs before action
    /// </summary>
    /// <param name="actionContext"></param>
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
      if (HttpContext.Current == null)
      {
        if (actionContext.Request.Properties.ContainsKey("MS_HttpContext"))
        {
          HttpContext.Current = ((HttpContextWrapper)actionContext.Request.Properties["MS_HttpContext"]).ApplicationInstance.Context;
        }
      }
    }
  }

Hope this helps.

J

JCallico

I followed @LachlanB approach and indeed the session was available when the session cookie was present on the request. The missing part is how the Session cookie is sent to the client the first time?

I created a HttpModule which not only enabling the HttpSessionState availability but also sends the cookie to the client when a new session is created.

public class WebApiSessionModule : IHttpModule
{
    private static readonly string SessionStateCookieName = "ASP.NET_SessionId";

    public void Init(HttpApplication context)
    {
        context.PostAuthorizeRequest += this.OnPostAuthorizeRequest;
        context.PostRequestHandlerExecute += this.PostRequestHandlerExecute;
    }

    public void Dispose()
    {
    }

    protected virtual void OnPostAuthorizeRequest(object sender, EventArgs e)
    {
        HttpContext context = HttpContext.Current;

        if (this.IsWebApiRequest(context))
        {
            context.SetSessionStateBehavior(SessionStateBehavior.Required);
        }
    }

    protected virtual void PostRequestHandlerExecute(object sender, EventArgs e)
    {
        HttpContext context = HttpContext.Current;

        if (this.IsWebApiRequest(context))
        {
            this.AddSessionCookieToResponseIfNeeded(context);
        }
    }

    protected virtual void AddSessionCookieToResponseIfNeeded(HttpContext context)
    {
        HttpSessionState session = context.Session;

        if (session == null)
        {
            // session not available
            return;
        }

        if (!session.IsNewSession)
        {
            // it's safe to assume that the cookie was
            // received as part of the request so there is
            // no need to set it
            return;
        }

        string cookieName = GetSessionCookieName();
        HttpCookie cookie = context.Response.Cookies[cookieName];
        if (cookie == null || cookie.Value != session.SessionID)
        {
            context.Response.Cookies.Remove(cookieName);
            context.Response.Cookies.Add(new HttpCookie(cookieName, session.SessionID));
        }
    }

    protected virtual string GetSessionCookieName()
    {
        var sessionStateSection = (SessionStateSection)ConfigurationManager.GetSection("system.web/sessionState");

        return sessionStateSection != null && !string.IsNullOrWhiteSpace(sessionStateSection.CookieName) ? sessionStateSection.CookieName : SessionStateCookieName;
    }

    protected virtual bool IsWebApiRequest(HttpContext context)
    {
        string requestPath = context.Request.AppRelativeCurrentExecutionFilePath;

        if (requestPath == null)
        {
            return false;
        }

        return requestPath.StartsWith(WebApiConfig.UrlPrefixRelative, StringComparison.InvariantCultureIgnoreCase);
    }
}

This works great. This keeps the session the same between requests as long as it hasn't timed out. Not sure if I am going to use it in prod just yet until I figure out a good way to switch the session state between required and read only to stop request blocking, but this has given me the starting path that I desire. Thank you!

m

maxisam

one thing need to mention on @LachlanB 's answer.

protected void Application_PostAuthorizeRequest()
    {
        if (IsWebApiRequest())
        {
            HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
        }
    }

If you omit the line if (IsWebApiRequest())

The whole site will have page loading slowness issue if your site is mixed with web form pages.

S

Sulabh Singla

Yes, session doesn't go hand in hand with Rest API and also we should avoid this practices. But as per requirements we need to maintain session somehow such that in every request client server can exchange or maintain state or data. So, the best way to achieve this without breaking the REST protocols is communicate through token like JWT.

https://jwt.io/

A

Andy A.

Going back to basics why not keep it simple and store the Session value in a hidden html value to pass to your API?

Controller

public ActionResult Index()
        {

            Session["Blah"] = 609;

            YourObject yourObject = new YourObject();
            yourObject.SessionValue = int.Parse(Session["Blah"].ToString());

            return View(yourObject);
        }

cshtml

@model YourObject

@{
    var sessionValue = Model.SessionValue;
}

<input type="hidden" value="@sessionValue" id="hBlah" />

Javascript

$(document).ready(function () {

    var sessionValue = $('#hBlah').val();

    alert(sessionValue);

    /* Now call your API with the session variable */}

}

Waht if the application uses both MVC and WebAPI? Also, it is more reasonable some things to be stored at server side, e. g. Sharepoint security tokens. Instead of implementing a special wrapper for tokens storage like azure blobs container, sometimes is reasonable reuse Session for this type of data. The Sharepoint security context as it implemented in app template, uses the session to store these security contexts, and only small pieces of data being transfered (session tag) instead of few kilobytes of data. It would be awesome if these context would be smaller...

Accessing Session Using ASP.NET Web API

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