This post shows how to implement localization in IdentityServer4 when using the Implicit Flow with an Angular client.

Code: https://github.com/damienbod/AspNet5IdentityServerAngularImplicitFlow

The problem

When the oidc implicit client calls the endpoint /connect/authorize to authenticate and authorize the client and the identity, the user is redirected to the AccountController login method using the IdentityServer4 package. If the culture and the ui-culture is set using the query string or using the default localization filter, it gets ignored in the host. By using a localization cookie, which is set from the client SPA application, it is possible to use this culture in IdentityServer4 and it’s host.

Part 2 IdentityServer4 Localization using ui_locales and the query string

IdentityServer 4 Localization

The ASP.NET Core localization is configured in the startup method of the IdentityServer4 host. The localization service, the resource paths and the RequestCultureProviders are configured here. A custom LocalizationCookieProvider is added to handle the localization cookie. The MVC middleware is then configured to use the localization.

public void ConfigureServices(IServiceCollection services)
{
	...

	services.AddSingleton<LocService>();
	services.AddLocalization(options => options.ResourcesPath = "Resources");

	services.AddAuthentication();

	services.AddIdentity<ApplicationUser, IdentityRole>()
	.AddEntityFrameworkStores<ApplicationDbContext>();

	services.Configure<RequestLocalizationOptions>(
		options =>
		{
			var supportedCultures = new List<CultureInfo>
				{
					new CultureInfo("en-US"),
					new CultureInfo("de-CH"),
					new CultureInfo("fr-CH"),
					new CultureInfo("it-CH")
				};

			options.DefaultRequestCulture = new RequestCulture(culture: "de-CH", uiCulture: "de-CH");
			options.SupportedCultures = supportedCultures;
			options.SupportedUICultures = supportedCultures;

			options.RequestCultureProviders.Clear();
			var provider = new LocalizationCookieProvider
			{
				CookieName = "defaultLocale"
			};
			options.RequestCultureProviders.Insert(0, provider);
		});

	services.AddMvc()
	 .AddViewLocalization()
	 .AddDataAnnotationsLocalization(options =>
	 {
		 options.DataAnnotationLocalizerProvider = (type, factory) =>
		 {
			 var assemblyName = new AssemblyName(typeof(SharedResource).GetTypeInfo().Assembly.FullName);
			 return factory.Create("SharedResource", assemblyName.Name);
		 };
	 });

	...

	services.AddIdentityServer()
		.AddSigningCredential(cert)
		.AddInMemoryIdentityResources(Config.GetIdentityResources())
		.AddInMemoryApiResources(Config.GetApiResources())
		.AddInMemoryClients(Config.GetClients())
		.AddAspNetIdentity<ApplicationUser>()
		.AddProfileService<IdentityWithAdditionalClaimsProfileService>();
}

The localization is added to the pipe in the Configure method.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
	...

	var locOptions = app.ApplicationServices.GetService<IOptions<RequestLocalizationOptions>>();
	app.UseRequestLocalization(locOptions.Value);

	app.UseStaticFiles();

	app.UseIdentityServer();

	app.UseMvc(routes =>
	{
		routes.MapRoute(
			name: "default",
			template: "{controller=Home}/{action=Index}/{id?}");
	});
}

The LocalizationCookieProvider class implements the RequestCultureProvider to handle the localization sent from the Angular client as a cookie. The class uses the defaultLocale cookie to set the culture. This was configured in the startup class previously.

using Microsoft.AspNetCore.Localization;
using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;

namespace IdentityServerWithIdentitySQLite
{
    public class LocalizationCookieProvider : RequestCultureProvider
    {
        public static readonly string DefaultCookieName = ".AspNetCore.Culture";

        public string CookieName { get; set; } = DefaultCookieName;

        /// <inheritdoc />
        public override Task<ProviderCultureResult> DetermineProviderCultureResult(HttpContext httpContext)
        {
            if (httpContext == null)
            {
                throw new ArgumentNullException(nameof(httpContext));
            }

            var cookie = httpContext.Request.Cookies[CookieName];

            if (string.IsNullOrEmpty(cookie))
            {
                return NullProviderCultureResult;
            }

            var providerResultCulture = ParseCookieValue(cookie);

            return Task.FromResult(providerResultCulture);
        }

        public static ProviderCultureResult ParseCookieValue(string value)
        {
            if (string.IsNullOrWhiteSpace(value))
            {
                return null;
            }

            var cultureName = value;
            var uiCultureName = value;

            if (cultureName == null && uiCultureName == null)
            {
                // No values specified for either so no match
                return null;
            }

            if (cultureName != null && uiCultureName == null)
            {
                uiCultureName = cultureName;
            }

            if (cultureName == null && uiCultureName != null)
            {
                cultureName = uiCultureName;
            }

            return new ProviderCultureResult(cultureName, uiCultureName);
        }
    }
}

The Account login view uses the localization to translate the different texts into one of the supported cultures.

@using System.Globalization
@using IdentityServerWithAspNetIdentity.Resources
@model IdentityServer4.Quickstart.UI.Models.LoginViewModel
@inject SignInManager<ApplicationUser> SignInManager

@inject LocService SharedLocalizer

@{
    ViewData["Title"] = @SharedLocalizer.GetLocalizedHtmlString("login");
}

<h2>@ViewData["Title"]</h2>
<div class="row">
    <div class="col-md-8">
        <section>
            <form asp-controller="Account" asp-action="Login" asp-route-returnurl="@Model.ReturnUrl" method="post" class="form-horizontal">
                <h4>@CultureInfo.CurrentCulture</h4>
                <hr />
                <div asp-validation-summary="All" class="text-danger"></div>
                <div class="form-group">
                    <label class="col-md-4 control-label">@SharedLocalizer.GetLocalizedHtmlString("email")</label>
                    <div class="col-md-8">
                        <input asp-for="Email" class="form-control" />
                        <span asp-validation-for="Email" class="text-danger"></span>
                    </div>
                </div>
                <div class="form-group">
                    <label class="col-md-4 control-label">@SharedLocalizer.GetLocalizedHtmlString("password")</label>
                    <div class="col-md-8">
                        <input asp-for="Password" class="form-control" type="password" />
                        <span asp-validation-for="Password" class="text-danger"></span>
                    </div>
                </div>
                <div class="form-group">
                    <label class="col-md-4 control-label">@SharedLocalizer.GetLocalizedHtmlString("rememberMe")</label>
                    <div class="checkbox col-md-8">
                        <input asp-for="RememberLogin" />
                    </div>
                </div>
                <div class="form-group">
                    <div class="col-md-offset-4 col-md-8">
                        <button type="submit" class="btn btn-default">@SharedLocalizer.GetLocalizedHtmlString("login")</button>
                    </div>
                </div>
                <p>
                    <a asp-action="Register" asp-route-returnurl="@Model.ReturnUrl">@SharedLocalizer.GetLocalizedHtmlString("registerAsNewUser")</a>
                </p>
                <p>
                    <a asp-action="ForgotPassword">@SharedLocalizer.GetLocalizedHtmlString("forgotYourPassword")</a>
                </p>
            </form>
        </section>
    </div>
</div>

@section Scripts {
    @{ await Html.RenderPartialAsync("_ValidationScriptsPartial"); }
}

The LocService uses the IStringLocalizerFactory interface to configure a shared resource for the resources.

using Microsoft.Extensions.Localization;
using System.Reflection;

namespace IdentityServerWithAspNetIdentity.Resources
{
    public class LocService
    {
        private readonly IStringLocalizer _localizer;

        public LocService(IStringLocalizerFactory factory)
        {
            var type = typeof(SharedResource);
            var assemblyName = new AssemblyName(type.GetTypeInfo().Assembly.FullName);
            _localizer = factory.Create("SharedResource", assemblyName.Name);
        }

        public LocalizedString GetLocalizedHtmlString(string key)
        {
            return _localizer[key];
        }
    }
}

Client Localization

The Angular SPA client uses the angular-l10n the localize the application.

 "dependencies": {
    "angular-l10n": "^4.0.0",

the angular-l10n is configured in the app module and is configured to save the current culture in a cookie called defaultLocale. This cookie matches what was configured on the server.

...

import { L10nConfig, L10nLoader, TranslationModule, StorageStrategy, ProviderType } from 'angular-l10n';

const l10nConfig: L10nConfig = {
    locale: {
        languages: [
            { code: 'en', dir: 'ltr' },
            { code: 'it', dir: 'ltr' },
            { code: 'fr', dir: 'ltr' },
            { code: 'de', dir: 'ltr' }
        ],
        language: 'en',
        storage: StorageStrategy.Cookie
    },
    translation: {
        providers: [
            { type: ProviderType.Static, prefix: './i18n/locale-' }
        ],
        caching: true,
        missingValue: 'No key'
    }
};

@NgModule({
    imports: [
        BrowserModule,
        FormsModule,
        routing,
        HttpClientModule,
        TranslationModule.forRoot(l10nConfig),
		DataEventRecordsModule,
        AuthModule.forRoot(),
    ],
    declarations: [
        AppComponent,
        ForbiddenComponent,
        HomeComponent,
        UnauthorizedComponent,
        SecureFilesComponent
    ],
    providers: [
        OidcSecurityService,
        SecureFileService,
        Configuration
    ],
    bootstrap:    [AppComponent],
})

export class AppModule {

    clientConfiguration: any;

    constructor(
        public oidcSecurityService: OidcSecurityService,
        private http: HttpClient,
        configuration: Configuration,
        public l10nLoader: L10nLoader
    ) {
        this.l10nLoader.load();

        console.log('APP STARTING');
        this.configClient().subscribe((config: any) => {
            this.clientConfiguration = config;

            let openIDImplicitFlowConfiguration = new OpenIDImplicitFlowConfiguration();
            openIDImplicitFlowConfiguration.stsServer = this.clientConfiguration.stsServer;
            openIDImplicitFlowConfiguration.redirect_url = this.clientConfiguration.redirect_url;
            // The Client MUST validate that the aud (audience) Claim contains its client_id value registered at the Issuer identified by the iss (issuer) Claim as an audience.
            // The ID Token MUST be rejected if the ID Token does not list the Client as a valid audience, or if it contains additional audiences not trusted by the Client.
            openIDImplicitFlowConfiguration.client_id = this.clientConfiguration.client_id;
            openIDImplicitFlowConfiguration.response_type = this.clientConfiguration.response_type;
            openIDImplicitFlowConfiguration.scope = this.clientConfiguration.scope;
            openIDImplicitFlowConfiguration.post_logout_redirect_uri = this.clientConfiguration.post_logout_redirect_uri;
            openIDImplicitFlowConfiguration.start_checksession = this.clientConfiguration.start_checksession;
            openIDImplicitFlowConfiguration.silent_renew = this.clientConfiguration.silent_renew;
            openIDImplicitFlowConfiguration.post_login_route = this.clientConfiguration.startup_route;
            // HTTP 403
            openIDImplicitFlowConfiguration.forbidden_route = this.clientConfiguration.forbidden_route;
            // HTTP 401
            openIDImplicitFlowConfiguration.unauthorized_route = this.clientConfiguration.unauthorized_route;
            openIDImplicitFlowConfiguration.log_console_warning_active = this.clientConfiguration.log_console_warning_active;
            openIDImplicitFlowConfiguration.log_console_debug_active = this.clientConfiguration.log_console_debug_active;
            // id_token C8: The iat Claim can be used to reject tokens that were issued too far away from the current time,
            // limiting the amount of time that nonces need to be stored to prevent attacks.The acceptable range is Client specific.
            openIDImplicitFlowConfiguration.max_id_token_iat_offset_allowed_in_seconds = this.clientConfiguration.max_id_token_iat_offset_allowed_in_seconds;

            configuration.FileServer = this.clientConfiguration.apiFileServer;
            configuration.Server = this.clientConfiguration.apiServer;

            this.oidcSecurityService.setupModule(openIDImplicitFlowConfiguration);

            // if you need custom parameters
            // this.oidcSecurityService.setCustomRequestParameters({ 'culture': 'fr-CH', 'ui-culture': 'fr-CH', 'ui_locales': 'fr-CH' });
        });
    }

    configClient() {

        console.log('window.location', window.location);
        console.log('window.location.href', window.location.href);
        console.log('window.location.origin', window.location.origin);
        console.log(`${window.location.origin}/api/ClientAppSettings`);

        return this.http.get(`${window.location.origin}/api/ClientAppSettings`);
    }
}

When the applications are started, the user can select a culture and login.

And the login view is localized correctly in de-CH

Or in french, if the culture is fr-CH

Links:

https://damienbod.com/2017/11/11/identityserver4-localization-using-ui_locales-and-the-query-string/

https://damienbod.com/2017/11/01/shared-localization-in-asp-net-core-mvc/

https://github.com/IdentityServer/IdentityServer4

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/localization

https://github.com/robisim74/angular-l10n