ASP.NET Identity 2.0 decrypt Owin cookie

Question

I'm working in a server-side application where I'm applying multi tenancy. In this server side I have a Backoffice (ASP.NET MVC) and a BackEnd (WCF).

I want to decrypt Identity cookie so that I can check that it is valid and use it to auth in WCF Services.

To be more specific I really want to know if ASP.NET Identity API provides any kind of service like the following example (it would work if I was using forms Authentication)

FormsAuthenticationTicket formsTicket = FormsAuthentication.Decrypt(tokenValue);

Thanks in advance.

Answer 1

After a lot of research I found a way to do this in a blog. The final algorithm looks like the following:

      private bool BackOfficeUserAuthorized(string ticket)
      {
        ticket = ticket.Replace('-', '+').Replace('_', '/');

        var padding = 3 - ((ticket.Length + 3) % 4);
        if (padding != 0)
            ticket = ticket + new string('=', padding);

        var bytes = Convert.FromBase64String(ticket);

        bytes = System.Web.Security.MachineKey.Unprotect(bytes,
            "Microsoft.Owin.Security.Cookies.CookieAuthenticationMiddleware",
                "ApplicationCookie", "v1");

        using (var memory = new MemoryStream(bytes))
        {
            using (var compression = new GZipStream(memory,
                                                CompressionMode.Decompress))
            {
                using (var reader = new BinaryReader(compression))
                {
                    reader.ReadInt32();
                    string authenticationType = reader.ReadString();
                    reader.ReadString();
                    reader.ReadString();

                    int count = reader.ReadInt32();

                    var claims = new Claim[count];
                    for (int index = 0; index != count; ++index)
                    {
                        string type = reader.ReadString();
                        type = type == "\0" ? ClaimTypes.Name : type;

                        string value = reader.ReadString();

                        string valueType = reader.ReadString();
                        valueType = valueType == "\0" ?
                                       "http://www.w3.org/2001/XMLSchema#string" :
                                         valueType;

                        string issuer = reader.ReadString();
                        issuer = issuer == "\0" ? "LOCAL AUTHORITY" : issuer;

                        string originalIssuer = reader.ReadString();
                        originalIssuer = originalIssuer == "\0" ?
                                                     issuer : originalIssuer;

                        claims[index] = new Claim(type, value,
                                               valueType, issuer, originalIssuer);
                    }

                    var identity = new ClaimsIdentity(claims, authenticationType,
                                                  ClaimTypes.Name, ClaimTypes.Role);

                    var principal = new ClaimsPrincipal(identity);

                    return principal.Identity.IsAuthenticated;
                }
            }
        }
    }

Be aware that principal is like if on the side that sends the auth cookie you just call:

HttpContext.Current.User

If you are interested in know how the algorithm works you can find it here