feat: implement authentication system for API Gateway and FileService

- Add JWT Bearer token validation to API Gateway with restricted CORS
- Add cookie-based JWT validation to FileService for browser image requests
- Create shared authentication infrastructure in FictionArchive.Service.Shared
- Update frontend to set fa_session cookie after OIDC login
- Add [Authorize] attributes to GraphQL mutations with role-based restrictions
- Configure OIDC settings for both services in docker-compose

Implements FA-17: Authentication for microservices architecture

FictionArchive.Service.Shared/Extensions/AuthenticationExtensions.cs

@@ -0,0 +1,91 @@
+using Microsoft.AspNetCore.Authentication.JwtBearer;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Configuration;
+using Microsoft.IdentityModel.Tokens;
+using FictionArchive.Service.Shared.Models.Authentication;
+
+namespace FictionArchive.Service.Shared.Extensions;
+
+public static class AuthenticationExtensions
+{
+    public static IServiceCollection AddOidcAuthentication(this IServiceCollection services, IConfiguration configuration)
+    {
+        var oidcConfig = configuration.GetSection("OIDC").Get<OidcConfiguration>();
+        
+        if (oidcConfig == null)
+        {
+            throw new InvalidOperationException("OIDC configuration is required but not found in app settings");
+        }
+
+        services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
+            .AddJwtBearer(options =>
+            {
+                options.Authority = oidcConfig.Authority;
+                options.Audience = oidcConfig.Audience;
+                options.RequireHttpsMetadata = !string.IsNullOrEmpty(oidcConfig.Authority) && oidcConfig.Authority.StartsWith("https://");
+
+                options.TokenValidationParameters = new TokenValidationParameters
+                {
+                    ValidateIssuer = oidcConfig.ValidateIssuer,
+                    ValidateAudience = oidcConfig.ValidateAudience,
+                    ValidateLifetime = oidcConfig.ValidateLifetime,
+                    ValidateIssuerSigningKey = oidcConfig.ValidateIssuerSigningKey,
+                    ClockSkew = TimeSpan.FromMinutes(5)
+                };
+            });
+
+        return services;
+    }
+
+    public static IServiceCollection AddOidcCookieAuthentication(this IServiceCollection services, IConfiguration configuration, string cookieName = "fa_session")
+    {
+        var oidcConfig = configuration.GetSection("OIDC").Get<OidcConfiguration>();
+        
+        if (oidcConfig == null)
+        {
+            throw new InvalidOperationException("OIDC configuration is required but not found in app settings");
+        }
+
+        services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
+            .AddJwtBearer(options =>
+            {
+                options.Authority = oidcConfig.Authority;
+                options.Audience = oidcConfig.Audience;
+                options.RequireHttpsMetadata = !string.IsNullOrEmpty(oidcConfig.Authority) && oidcConfig.Authority.StartsWith("https://");
+
+                options.Events = new JwtBearerEvents
+                {
+                    OnMessageReceived = context =>
+                    {
+                        // Try to get token from cookie first, then from Authorization header
+                        if (context.Request.Cookies.ContainsKey(cookieName))
+                        {
+                            context.Token = context.Request.Cookies[cookieName];
+                        }
+
+                        return Task.CompletedTask;
+                    }
+                };
+
+                options.TokenValidationParameters = new TokenValidationParameters
+                {
+                    ValidateIssuer = oidcConfig.ValidateIssuer,
+                    ValidateAudience = oidcConfig.ValidateAudience,
+                    ValidateLifetime = oidcConfig.ValidateLifetime,
+                    ValidateIssuerSigningKey = oidcConfig.ValidateIssuerSigningKey,
+                    ClockSkew = TimeSpan.FromMinutes(5)
+                };
+            });
+
+        return services;
+    }
+
+    public static IServiceCollection AddFictionArchiveAuthorization(this IServiceCollection services)
+    {
+        services.AddAuthorizationBuilder()
+            .AddPolicy("Admin", policy => policy.RequireRole("admin"))
+            .AddPolicy("User", policy => policy.RequireAuthenticatedUser());
+
+        return services;
+    }
+}

FictionArchive.Service.Shared/FictionArchive.Service.Shared.csproj

@@ -29,6 +29,7 @@
         <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="9.0.4" />
         <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL.NodaTime" Version="9.0.4" />
         <PackageReference Include="RabbitMQ.Client" Version="7.2.0" />
+        <PackageReference Include="Microsoft.AspNetCore.Authentication.JwtBearer" Version="8.0.11" />
     </ItemGroup>
     
     <ItemGroup>

FictionArchive.Service.Shared/Models/Authentication/OidcConfiguration.cs

@@ -0,0 +1,12 @@
+namespace FictionArchive.Service.Shared.Models.Authentication;
+
+public class OidcConfiguration
+{
+    public string Authority { get; set; } = string.Empty;
+    public string ClientId { get; set; } = string.Empty;
+    public string Audience { get; set; } = string.Empty;
+    public bool ValidateIssuer { get; set; } = true;
+    public bool ValidateAudience { get; set; } = true;
+    public bool ValidateLifetime { get; set; } = true;
+    public bool ValidateIssuerSigningKey { get; set; } = true;
+}