OpenIdConnect with .NET Core 2.2 MVC towards IdentityServer3 using ScopePolicy. How do you get scopes into user principal? - asp.net-core

Question

It seems to set up OpenIdConnect authentication from .NET Core 2.2 to IdentityServer3 I have to setup through generic AddOpenIdConnect() call, and in order for scope policy to work, I have overridden OnTokenValidated, where I parse the access token received, and add the scopes in it to the ClaimsPrincipal object.
I have found no other way of getting scope policy to work. This seems a bit hackish though. Is there a better or simpler way, so I don't need to override events, or at least not parse the access token? It is parsed in the framework anyhow, so I would suspect there were other functionality available to get scopes into the claims principal.
Moving our code from .NET 4.5.2 to .NET Core 2.2, I need to set up authentication towards our IdentityServer3 server in a very different way.
I was hoping new functionality in later framework allowed for simple setup of authentication towards IdentityServer3, but I've found no fitting example.
I saw someone saying that IdentityServer4.AccessTokenValidation NuGet package could work towards IdentityServer3, but only example I've found has been with simple JWT authentication not allowing implicit user login flow.
Consequently, I've ended up using standard ASP.NET Core libraries to set up openidconnect, and then I need to tweak the code to make it work.
Not sure if the code below handles all it needs to, but at least I've gotten where I can log in and use the new web site, and write cypress tests. Any suggestions on how to do this better or simpler would be appreciated.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseAuthentication();
app.UseMvc();
}
public void ConfigureServices(IServiceCollection services)
{
// Without this, I get "Correlation failed." error from Microsoft.AspNetCore.Authentication.RemoteAuthenticationHandler`1.HandleRequestAsync()
services.Configure<CookiePolicyOptions>(options =>
{
options.CheckConsentNeeded = context => true;
options.MinimumSameSitePolicy = SameSiteMode.None;
});
services.AddAuthentication(o => {
o.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
o.DefaultChallengeScheme = OpenIdConnectDefaults.AuthenticationScheme;
}).AddCookie().AddOpenIdConnect(o =>
{
o.Authority = "https://myidentityserver3.myfirm.com";
o.ClientId = "myidentityserver3clientname";
o.SignedOutRedirectUri = "https://localhost:50011/signout";
o.ResponseType = "id_token token";
o.SaveTokens = true;
o.Scope.Add("openid");
o.Scope.Add("roles");
o.Scope.Add("profile");
o.Scope.Add("customrequiredscopeforapi");
o.GetClaimsFromUserInfoEndpoint = false;
{
var old = o.Events.OnTokenValidated;
o.Events.OnTokenValidated = async ctx =>
{
if (old != null) await old(ctx);
var token = MyCustomAuthUtils.ParseBearerToken(ctx.ProtocolMessage.AccessToken);
foreach (var scope in token.Scopes)
{
ctx.Principal.AddIdentity(new ClaimsIdentity(new[] { new Claim("Scope", scope) }));
}
// Our controllers need access token to call other web api's, so putting it here.
// Not sure if that is a good way to do it.
ctx.Principal.AddIdentity(new ClaimsIdentity(new[] { new Claim("access_token", ctx.ProtocolMessage.AccessToken) }));
};
}
});
var mvcBuilder = services.AddMvc(o =>
{
o.Filters.Add(new AuthorizeFilter(ScopePolicy.Create("customrequiredscopeforapi")));
});
services.AddAuthorization();
}

Answer 1

The first thing is you don't need to manally decode the access token , just use ctx.SecurityToken.Claims in OnTokenValidated event to get all claims included in the token .
I'm not sure why you need to use scope to identify the permission . The scope parameter in the OIDC-conformant pipeline determines:
The permissions that an authorized application should have for a given resource server
Which standard profile claims should be included in the ID Token (if the user consents to provide this information to the application)
You can use role to identify whether current login user could access the protected resource . And the OpenID Connect middleware will help mapping the role claim to claim principle .