Split Site:Audience into Site:ExternalUrl + Site:CorsAllowedOrigins

The Site:Audience setting was conflating two distinct concepts: an OAuth
JWT audience (a single resource identifier) and a CORS allow-list (an
array of origins). Collapsing them caused several latent bugs:
- OAuth/JWT validation expected a single string while CORS WithOrigins
  accepts an array.
- Password-reset callback URLs and OAuth client RedirectUri/Origin were
  being built from what was meant to be an audience identifier, not a
  base URL.
- Yavsc.Org's main CORS policy was hardcoded to '*', with no way to
  restrict it without code changes.

Changes:
- SiteSettings.Audience (string) replaced with CorsAllowedOrigins
  (IList<string>).
- OAuth JWT Authority still reads Site:Authority; Audience now reads
  Site:ExternalUrl (Org only; Api/Blogs use ValidateAudience=false).
- MailSender and AccountController build reset-callback URLs from
  Site:ExternalUrl.
- ClientController uses Site:ExternalUrl for OAuth RedirectUri/Origin
  defaults on newly created clients.
- Yavsc.Api and Yavsc.Blogs now read CORS origins from
  Site:CorsAllowedOrigins instead of hardcoded URLs.

Add shared AddYavscCors / AddYavscJwtBearer extension methods in
Yavsc.Server/Helpers/ServiceExtensions.cs to enforce a single
configuration contract across all runtime services (Api, Blogs, Org).
Fails closed when CorsAllowedOrigins is empty; fails fast at startup
when Site:Authority is missing.

Remove obsolete ConfigurationHelpers.GetAudience (no remaining callers).

Local appsettings-*.json files (which carry deployment-specific values
and are gitignored) must be updated to add Site:CorsAllowedOrigins.

src/Yavsc.Server/Helpers/Configuration.cs

@@ -12,10 +12,4 @@ public static class ConfigurationHelpers
         return builder.Configuration.GetSection("Site")
                 .GetValue<string>("Authority");
     }
-    public static string GetAudience(this WebApplicationBuilder builder)
-    {
-        return builder.Configuration.GetSection("Site")
-                .GetValue<string>("Audience");
-    }
-
 }

src/Yavsc.Server/Helpers/ServiceExtensions.cs

@@ -0,0 +1,97 @@
+using Microsoft.AspNetCore.Authentication;
+using Microsoft.AspNetCore.Authentication.JwtBearer;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.IdentityModel.Tokens;
+
+namespace Yavsc.Server.Helpers;
+
+/// <summary>
+/// Shared service registration helpers for Yavsc runtime services (Api, Blogs, Org, ...).
+///
+/// Conventions: every service reads its CORS origin allow-list from
+/// <c>Site:CorsAllowedOrigins</c> as a JSON array, and its JWT Bearer authority
+/// from <c>Site:Authority</c>. These helpers enforce that contract so a service
+/// only needs to opt-in via a single line.
+/// </summary>
+public static class ServiceExtensions
+{
+    /// <summary>
+    /// Default policy name used across all Yavsc runtime services.
+    /// </summary>
+    public const string DefaultCorsPolicyName = "default";
+
+    /// <summary>
+    /// Register the shared <c>"default"</c> CORS policy, sourcing the allow-list
+    /// from <c>Site:CorsAllowedOrigins</c>. Fails closed (no origins registered)
+    /// when the array is missing or empty.
+    /// </summary>
+    /// <param name="services">The service collection to add CORS to.</param>
+    /// <param name="configuration">Configuration root, used to read <c>Site:CorsAllowedOrigins</c>.</param>
+    /// <param name="policyName">Optional policy name override (defaults to <see cref="DefaultCorsPolicyName"/>).</param>
+    /// <returns>The same <paramref name="services"/> instance for chaining.</returns>
+    public static IServiceCollection AddYavscCors(
+        this IServiceCollection services,
+        IConfiguration configuration,
+        string policyName = DefaultCorsPolicyName)
+    {
+        var allowedOrigins = configuration
+            .GetSection("Site:CorsAllowedOrigins")
+            .Get<string[]>() ?? Array.Empty<string>();
+
+        services.AddCors(options =>
+        {
+            options.AddPolicy(policyName, policy =>
+            {
+                if (allowedOrigins.Length == 0)
+                {
+                    // Fail closed: with no origins configured, don't fall back to "*".
+                    // The policy ends up effectively denying cross-origin requests,
+                    // which is the safe default.
+                    return;
+                }
+                policy.WithOrigins(allowedOrigins)
+                    .AllowAnyHeader()
+                    .AllowAnyMethod();
+            });
+        });
+
+        return services;
+    }
+
+    /// <summary>
+    /// Register the standard Yavsc JWT Bearer authentication scheme, sourcing
+    /// the authority from <c>Site:Authority</c>. Throws at startup if the
+    /// configuration is missing — this is intentional, we'd rather fail to
+    /// boot than accept tokens from an unconfigured issuer.
+    /// </summary>
+    /// <param name="builder">The authentication builder to extend.</param>
+    /// <param name="configuration">Configuration root, used to read <c>Site:Authority</c>.</param>
+    /// <param name="configure">Optional callback for service-specific options
+    /// (e.g. setting <c>options.Audience</c> in <c>Yavsc.Org</c>).</param>
+    /// <param name="schemeName">Optional scheme name override (defaults to <c>"Bearer"</c>).</param>
+    /// <returns>The same authentication builder, for chaining.</returns>
+    public static AuthenticationBuilder AddYavscJwtBearer(
+        this AuthenticationBuilder builder,
+        IConfiguration configuration,
+        Action<JwtBearerOptions>? configure = null,
+        string schemeName = "Bearer")
+    {
+        var authority = configuration.GetSection("Site")["Authority"]
+            ?? throw new InvalidOperationException(
+                "Site:Authority is required to configure Yavsc JWT Bearer authentication.");
+
+        return builder.AddJwtBearer(schemeName, options =>
+        {
+            options.IncludeErrorDetails = true;
+            options.Authority = authority;
+            options.TokenValidationParameters = new TokenValidationParameters
+            {
+                ValidateAudience = false,
+                RoleClaimType = YavscConstants.RoleClaimType
+            };
+            options.MapInboundClaims = true;
+            configure?.Invoke(options);
+        });
+    }
+}

src/Yavsc.Server/Services/MailSender.cs

@@ -97,7 +97,7 @@ namespace Yavsc.Services
 
         public async Task SendPasswordResetCodeAsync(ApplicationUser user, string email, string resetCode)
         {
-            var callbackUrl = siteSettings.Audience + "/Account/ResetPassword/" +
+            var callbackUrl = siteSettings.ExternalUrl + "/Account/ResetPassword/" +
                     HttpUtility.UrlEncode(user.Id) + "/" + HttpUtility.UrlEncode(resetCode);
 
             await SendEmailAsync(user.UserName, user.Email,

src/Yavsc.Server/Settings/SiteSettings.cs

@@ -14,10 +14,14 @@ namespace Yavsc
         public string FavIcon { get; set; } = "favicon.ico";
         public string Logo { get; set; } = "logo.png";
         /// <summary>
+        /// Origins to allow via the CORS "default" policy.
+        /// Each entry must be a full origin (scheme + host [+ port]), e.g. "https://app.example.com".
         /// </summary>
-        /// <returns></returns>
-        public string Audience { get; set; } = "lua.pschneider.fr";
-       
+        public IList<string> CorsAllowedOrigins { get; set; } = new List<string>
+        {
+            "https://localhost:5001"
+        };
+
         /// <summary>
         /// External Url
         /// </summary>

src/Yavsc.Server/Yavsc.Server.csproj

@@ -15,6 +15,7 @@
     <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" />
     <PackageReference Include="HigginsSoft.IdentityServer8" />
     <PackageReference Include="Microsoft.AspNetCore.Identity.EntityFrameworkCore" />
+    <PackageReference Include="Microsoft.AspNetCore.Authentication.JwtBearer" />
     <PackageReference Include="Microsoft.AspNetCore.Identity.UI" />
     <PackageReference Include="Microsoft.AspNetCore.Http.Features" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Design">