Authorization Role/Policy Attributes Not Working In .Net Core 3 - asp.net-core

Question

I've had no luck getting any Role or Policy attributes working in .Net Core 3. I started my project with the .Net Core Angular starter project with authentication.
I figured this was something to do with the new .AddDefault methods so I have simplified it as much as I possibly can and it still doesn't work.
Here is my policy:
services.AddAuthorization(options =>
{
options.AddPolicy("IsAdmin", policy =>
policy.RequireClaim("role", "admin"));
});
Here is my controller:
[Authorize(Policy = "IsAdmin")]
[Route("api/[controller]")]
public class AdminController : Controller
{
...
I made a custom Profile service that adds the claim to the token,
var claims = new List<Claim>();
if (await _userManager.IsInRoleAsync(user, "Admin"))
{
claims.Add(new Claim(JwtClaimTypes.Role, "admin"));
}
context.IssuedClaims.AddRange(claims);
Inside my access token (from jwt.io):
Other parts of configure services:
services.AddDefaultIdentity<ApplicationUser>()
.AddRoles<IdentityRole>()
.AddEntityFrameworkStores<ApplicationDbContext>();
...
services.AddAuthentication()
.AddIdentityServerJwt();
The plain [Authorize] tag is working fine with the access token on other controllers.
When I hit this controller with the access token I get a 403 response
What am I missing that is preventing this from working?

Answer 1

I try your code and find that the role claim key has been transformed to the standard Role ClaimsType : http://schemas.microsoft.com/ws/2008/06/identity/claims/role
So using ClaimTypes.Role will fix the problem:
services.AddAuthorization(options => {
options.AddPolicy("IsAdmin", policy =>
{
policy.RequireClaim(ClaimTypes.Role,"admin");
});
});
Demo

Answer 2

You should also be able to achieve this without needing a policy. ASP.NET automatically maps common claims to the Microsoft schema.
When you inspect your access token. You will see you are sending the role claim. But when you look at the claims in the controller, you will notice that it has been transformed to http://schemas.microsoft.com/ws/2008/06/identity/claims/role.
There are two things you can do. Either set the RoleClaimType to ClaimTypes.Role. Like so:
services.Configure<JwtBearerOptions>(IdentityServerJwtConstants.IdentityServerJwtBearerScheme, options => {
options.TokenValidationParameters.RoleClaimType = ClaimTypes.Role;
});
Or tell the JwtSecurityTokenHandler not to map default inbound claims like this:
JwtSecurityTokenHandler.DefaultMapInboundClaims = false;
Since it's a static property this can be done at any time. But I set it somewhere during my service registrations.