Implement base controller for shared functionality; update existing controllers to inherit from BaseController and adjust user ID handling. Add JWT authentication support and modify item retrieval methods in GameDataController.

Program.cs

@@ -1,4 +1,6 @@
+using Microsoft.AspNetCore.Authentication.JwtBearer;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.IdentityModel.Tokens;
 using PetCompanion.Data;
 using PetCompanion.Repositories;
 using PetCompanion.Services;
@@ -12,6 +14,10 @@ namespace PetCompanion
         {
             var builder = WebApplication.CreateBuilder(args);
 
+            // Read Firebase configuration from environment variables
+            var firebaseAppId = Environment.GetEnvironmentVariable("FIREBASE_APP_ID") ??
+                throw new InvalidOperationException("FIREBASE_APP_ID environment variable is not set");
+
             // Add services to the container.
             builder.Services.AddControllers()
                 .AddJsonOptions(options =>
@@ -57,6 +63,21 @@ namespace PetCompanion
                 });
             });
 
+            builder.Services
+                .AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
+                .AddJwtBearer(options =>
+                {
+                    options.Authority = $"https://securetoken.google.com/{firebaseAppId}";
+                    options.TokenValidationParameters = new TokenValidationParameters
+                    {
+                        ValidateIssuer = true,
+                        ValidIssuer = $"https://securetoken.google.com/{firebaseAppId}",
+                        ValidateAudience = true,
+                        ValidAudience = firebaseAppId,
+                        ValidateLifetime = true
+                    };
+                });
+
             var app = builder.Build();
 
             // Configure the HTTP request pipeline.
@@ -67,6 +88,8 @@ namespace PetCompanion
             }
 
             app.UseHttpsRedirection();
+
+            app.UseAuthentication();
             app.UseAuthorization();
 
             // After app builder is created