.net - How to know when OWIN cookie will expire?

Question

I would like to create some kind of countdown timer based on the time the OWIN cookie will expire. I am using OWIN with MVC 5 and from what I understand SlidingExpiration is on by default. I do not use 'session' as I need this app to live within a web farm (I dont plan on deploying a session database).

Answer 1

All you need is to get hold of the CookieValidateIdentityContext during the cookie validation stage. Once you get it, extract whatever you need and keep them as Claim or some other way that you prefer.

For MVC 5 with Asp.NET Identity 2.0, you need to perform two steps:

1. Define custom OnValidateIdentity, extract cookie information, and keep it as Claim.

   public class Startup
   {
     public void Configuration(IAppBuilder app)
     {
       app.UseCookieAuthentication(new CookieAuthenticationOptions
       {
         AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
         Provider = new CookieAuthenticationProvider
         {
           OnValidateIdentity = MyCustomValidateIdentity //refer to the implementation below
         }
       }
     }
   
   
     // this method will be called on every request
     // it is also one of the few places where you can access unencrypted cookie content as CookieValidateIdentityContext
     // once you get cookie information you need, keep it as one of the Claims
     // please ignore the MyUserManager and MyUser classes, they are only for sample, you should have yours
     private static Task MyCustomValidateIdentity(CookieValidateIdentityContext context)
     {
       // validate security stamp for 'sign out everywhere'
       // here I want to verify the security stamp in every 100 seconds.
       // but I choose not to regenerate the identity cookie, so I passed in NULL 
       var stampValidator = SecurityStampValidator.OnValidateIdentity<MyUserManager<Myuser>. MyUser>(TimeSpan.FromSeconds(100), null); 
       stampValidator.Invoke(context);
   
       // here we get the cookie expiry time
       var expireUtc = context.Properties.ExpiresUtc;
   
       // add the expiry time back to cookie as one of the claims, called 'myExpireUtc'
       // to ensure that the claim has latest value, we must keep only one claim
       // otherwise we will be having multiple claims with same type but different values
       var claimType = "myExpireUtc";
       var identity = context.Identity;
       if(identity.HasClaim(c=> c.Type == claimType))
       {
         var existingClaim = identity.FindFirst(claimType);
         identity.RemoveClaim(existingClaim); 
       }
       var newClaim = new Claim(claimType, expireUtc.Value.UtcTicks.ToString());
       context.Identity.AddClaim(newClaim);
   
       return Task.FromResult(0);
     }
   }
   

2. Access your Claim in your controller methods

   // since expiry time has now become part of your claims, you now can get it back easily
   // this example just returns the remaining time in total seconds, as a string value
   // assuming this method is part of your controller methods
   
   public string RemainingTime()
   {
     var identity = User.Identity as ClaimsIdentity;
     var claimType = "myExpireUtc";  //NOTE: must be the same key value "myExpireUtc" defined in code shown above
   
     if(identity != null && identity.HasClaim(c=> c.Type == claimType))
     { 
       var expireOn = identity.FindFirstValue(claimType); 
   
       DateTimeOffset currentUtc = DateTimeOffset.UtcNow;
       DateTimeOffset? expireUtc = new DateTimeOffset(long.Parse(expireOn), TimeSpan.Zero);
   
       var remaining = (expireUtc.Value - currentUtc).TotalSeconds;
   
       return remaining.ToString();
     }
     return string.Empty;
   }
   

I use this approach to remind my application users to extend their session before session time out.

Credit to this post How do I access Microsoft.Owin.Security.xyz OnAuthenticated context AddClaims values?