Add project files.

GoogleApi/Controllers/InternalController.cs

@@ -0,0 +1,83 @@
+using Microsoft.AspNetCore.Mvc;
+using GoogleApi.Models;
+using GoogleApi.Security;
+using GoogleApi.Services;
+
+namespace GoogleApi.Controllers;
+
+/// <summary>
+/// Internal API endpoint called by Gateway.
+/// Protected by X-Internal-Key header validation.
+/// </summary>
+[ApiController]
+[Route("internal")]
+public sealed class InternalController : ControllerBase
+{
+    private readonly GoogleAdsService _googleAds;
+    private readonly ILogger<InternalController> _logger;
+
+    public InternalController(GoogleAdsService googleAds, ILogger<InternalController> logger)
+    {
+        _googleAds = googleAds;
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Health check - no auth required.
+    /// </summary>
+    [HttpGet("health")]
+    public IActionResult Health()
+    {
+        _logger.LogDebug("[InternalController] Health check");
+        return Ok(new
+        {
+            ok = true,
+            service = "GoogleApi",
+            timestamp = DateTimeOffset.UtcNow
+        });
+    }
+
+    /// <summary>
+    /// Main execution endpoint - Gateway calls this.
+    /// Protected by InternalAuthFilter.
+    /// </summary>
+    [ServiceFilter(typeof(InternalAuthFilter))]
+    [HttpPost("execute")]
+    public async Task<IActionResult> Execute([FromBody] ProviderRequest request, CancellationToken ct)
+    {
+        _logger.LogInformation(
+            "[InternalController] Execute called | Operation={Operation} RequestId={RequestId}",
+            request?.Operation, request?.RequestId);
+
+        if (request == null)
+        {
+            return BadRequest(ProviderResponse.Fail(null, "VALIDATION", "Request body is required"));
+        }
+
+        if (string.IsNullOrWhiteSpace(request.Operation))
+        {
+            return BadRequest(ProviderResponse.Fail(request.RequestId, "VALIDATION", "Operation is required"));
+        }
+
+        var result = await _googleAds.ExecuteAsync(request, ct);
+
+        if (result.Ok)
+        {
+            return Ok(result);
+        }
+        else
+        {
+            // Use appropriate status codes based on error
+            var statusCode = result.Error?.Code switch
+            {
+                "VALIDATION" => 400,
+                "NOT_FOUND" => 404,
+                "UNAUTHORIZED" => 401,
+                "FORBIDDEN" => 403,
+                _ => 400
+            };
+
+            return StatusCode(statusCode, result);
+        }
+    }
+}