Any way to use Authorization Policies in a view in .NET Core 1.0 MVC?

Question

I know in controllers, you can write [Authorize("policyName")] without an issue, but is there any way to use a policy in a view? I'd rather not use User.IsInRole(...) every single time I want to authorize some HTML.

Edit:

Here's some code

Startup.cs -- Policy Declaration

    services.AddAuthorization(options =>
    {
        options.AddPolicy("testPolicy", policy =>
        {
            policy.RequireAuthenticatedUser()
                  .RequireRole("RoleOne", "RoleTwo", "RoleThree")
                  .RequireClaim(ClaimTypes.Email);
        });
    });

Admin Controller

[Authorize("testPolicy")]
public class AdminController : Controller
{
    public IActionResult Index()
    {
        return View();
    }
}

Navbar HTML

<div class="navbar navbar-inverse navbar-fixed-top">
            <div class="container">
                <div class="navbar-collapse collapse">
                    <ul class="nav navbar-nav">
                        <li><a asp-controller="Home" asp-action="Index">Home</a></li> 

                        <!-- I want to implement my policy here. -->
                        @if (User.IsInRole("..."))
                        {
                            <li><a asp-controller="Admin" asp-action="Index">Admin</a></li>
                        }
                    </ul>
                    @await Html.PartialAsync("_LoginPartial")
                </div>
            </div>

Answer 1

I found this link which may be helpful: https://docs.asp.net/en/latest/security/authorization/views.html

Examples from that page:

@if (await AuthorizationService.AuthorizeAsync(User, "PolicyName"))
{
    <p>This paragraph is displayed because you fulfilled PolicyName.</p>
}

In some cases the resource will be your view model, and you can call AuthorizeAsync in exactly the same way as you would check during resource based authorization;

@if (await AuthorizationService.AuthorizeAsync(User, Model, Operations.Edit))
{
    <p><a class="btn btn-default" role="button"
        href="@Url.Action("Edit", "Document", new {id= Model.Id})">Edit</a></p>
}

Answer 2

I ended up creating a tag helper to conditionally hide the element it's associated with.

[HtmlTargetElement(Attributes = "policy")]
public class PolicyTagHelper : TagHelper
{
    private readonly IAuthorizationService _authService;
    private readonly ClaimsPrincipal _principal;

    public PolicyTagHelper(IAuthorizationService authService, IHttpContextAccessor httpContextAccessor)
    {
        _authService = authService;
        _principal = httpContextAccessor.HttpContext.User;
    }

    public string Policy { get; set; }

    public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
    {
        // if (!await _authService.AuthorizeAsync(_principal, Policy)) ASP.NET Core 1.x
        if (!(await _authService.AuthorizeAsync(_principal, Policy)).Succeeded)
            output.SuppressOutput();
    }
}

Usage

<li policy="testPolicy"><a asp-controller="Admin" asp-action="Index">Admin</a></li>

Answer 3

This is one of the big improvements in ASP Core when you can inject the identity to all pages in the startup file:

@if (User.IsInRole("Admin"))
{
    <p>
    <a asp-action="Create" asp-controller="MyController">Create New</a>
</p>
}

In Startup.cs:

 services.AddIdentity<ApplicationUser, IdentityRole>()

EDIT: Ok I misread the post, you already knew this :) - ill leave it anyway if someone can use it.