Override Authorize Attribute in ASP.NET MVC

Edit: Since ASP.NET MVC 4 the best approach is simply to use the built-in AllowAnonymous attribute.

The answer below refers to earlier versions of ASP.NET MVC

You could create a custom authorisation attribute inheriting from the standard AuthorizeAttribute with an optional bool parameter to specify whether authorisation is required or not.

public class OptionalAuthorizeAttribute : AuthorizeAttribute
{
    private readonly bool _authorize;

    public OptionalAuthorizeAttribute()
    {
        _authorize = true;
    }

    public OptionalAuthorizeAttribute(bool authorize)
    {
        _authorize = authorize;
    }

    protected override bool AuthorizeCore(HttpContextBase httpContext)
    {
        if(!_authorize)
            return true;

                    return base.AuthorizeCore(httpContext);
    }
}

Then you can decorate your base controller with that attribute:

[OptionalAuthorize]
public class ControllerBase : Controller
{
}

and for any controllers you don't want authorisation simply use the override with a 'false' - e.g.

[OptionalAuthorize(false)]
public class TestController : ControllerBase
{
    public ActionResult Index()
    {
        return View();
    }
}

My personal take on this would be to split the controller. Just create another controller For the actions you don't need authentication.

Or you could have :

• BaseController
  doesn't require authentication - here you have all your "base stuff" :).

• BaseAuthController : BaseController
  all actions here require authentication.

That way you can have authentication when you want , just by deriving from a specific class.

If you just want one action to be unauthorized on an otherwise authorized controller you can do something like this:

public class RequiresAuthorizationAttribute : ActionFilterAttribute
{
    private readonly bool _authorize;

    public RequiresAuthorizationAttribute()
    {
        _authorize = true;
    }

    public RequiresAuthorizationAttribute(bool authorize)
    {
        _authorize = authorize;
    }

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        var overridingAttributes = filterContext.ActionDescriptor.GetCustomAttributes(typeof (RequiresAuthorizationAttribute), false);

        if (overridingAttributes.Length > 0 && overridingAttributes[0] as RequiresAuthorizationAttribute != null && !((RequiresAuthorizationAttribute)overridingAttributes[0])._authorize)
            return;

        if (_authorize)
        {
            //redirect if not authenticated
            if (!filterContext.HttpContext.User.Identity.IsAuthenticated)
            {
                //use the current url for the redirect
                var redirectOnSuccess = filterContext.HttpContext.Request.Url.AbsolutePath;

                //send them off to the login page
                //var redirectUrl = string.Format("?RedirectUrl={0}", redirectOnSuccess);
                var loginUrl = LinkBuilder.BuildUrlFromExpression<HomeController>(filterContext.RequestContext, RouteTable.Routes,
                                                                                  x => x.Login(redirectOnSuccess));
                filterContext.HttpContext.Response.Redirect(loginUrl, true);
            }
        }
    }
}