What is the burden of User.Identity.GetUserId()? - asp.net-mvc

Question

In my ASP.NET MVC applications I use User.Identity.GetUserId() abundantly. However, I wonder if this has severe performance penalties.
Alternatively, I believe I can do this: In a View, I can assign the current user's id to a hidden field in the first page load. Then, when making AJAX calls, I can pass the hidden field value to controllers' actions. This way, I would not need to use User.Identity.GetUserId() method to retrieve the userid of the current user.
I wonder if anyone has any ideas on this?

Answer 1

Take a look at the source for GetUserId extension method:
/// <summary>
/// Return the user id using the UserIdClaimType
/// </summary>
/// <param name="identity"></param>
/// <returns></returns>
public static string GetUserId(this IIdentity identity)
{
if (identity == null)
{
throw new ArgumentNullException("identity");
}
var ci = identity as ClaimsIdentity;
if (ci != null)
{
return ci.FindFirstValue(ClaimTypes.NameIdentifier);
}
return null;
}
/// <summary>
/// Return the claim value for the first claim with the specified type if it exists, null otherwise
/// </summary>
/// <param name="identity"></param>
/// <param name="claimType"></param>
/// <returns></returns>
public static string FindFirstValue(this ClaimsIdentity identity, string claimType)
{
if (identity == null)
{
throw new ArgumentNullException("identity");
}
var claim = identity.FindFirst(claimType);
return claim != null ? claim.Value : null;
}
Every time you call that extension method it searches the identity for the ClaimTypes.NameIdentifier claim.
The performance impact is not that substantial (IMO) but leaking user information in hidden (there not actually hidden if one can see them with one click of view source) is not a good idea.
If you are concerned about calling it multiple times and need it in multiple locations through out a request then you can have it lazy loaded behind a property in your controller or a base controller.
private string userId
public string UserId {
get {
if(userid == null) {
userid = User.Identity.GetUserId();
}
return userid;
}
}
You could also create a service to encapsulate that information.