Simple S3 client (#836)

This functionality is intended to be used to manage datasets for test cases, but may be useful elsewhere in the future.

- **Add S3 client with AWS Signature V4 (SigV4) signing** — new `S3Client` in `zenutil/cloud/` supporting `GetObject`, `PutObject`, `DeleteObject`, `HeadObject`, and `ListObjects` operations
- **Add EC2 IMDS credential provider** — automatically fetches and refreshes temporary AWS credentials from the EC2 Instance Metadata Service (IMDSv2) for use by the S3 client
- **Add SigV4 signing library** — standalone implementation of AWS Signature Version 4 request signing (headers and query-string presigning)
- **Add path-style addressing support** — enables compatibility with S3-compatible stores like MinIO (in addition to virtual-hosted style)
- **Add S3 integration tests** — includes a `MinioProcess` test helper that spins up a local MinIO server, plus integration tests exercising the S3 client end-to-end
- **Add S3-backed `HttpObjectStoreService` tests** — integration tests verifying the zenserver object store works against an S3 backend
- **Refactor mock IMDS into `zenutil/cloud/`** — moved and generalized the mock IMDS server from `zencompute` so it can be reused by both compute and S3 credential tests

2 files changed, 4 insertions, 108 deletions

diff --git a/src/zencompute/include/zencompute/cloudmetadata.h b/src/zencompute/include/zencompute/cloudmetadata.h
index a5bc5a34d..3b9642ac3 100644
--- a/src/zencompute/include/zencompute/cloudmetadata.h
+++ b/src/zencompute/include/zencompute/cloudmetadata.h
@@ -2,6 +2,8 @@
 
 #pragma once
 
+#include <zenutil/cloud/cloudprovider.h>
+
 #include <zencore/compactbinarybuilder.h>
 #include <zencore/logging.h>
 #include <zencore/thread.h>
@@ -13,16 +15,6 @@
 
 namespace zen::compute {
 
-enum class CloudProvider
-{
-	None,
-	AWS,
-	Azure,
-	GCP
-};
-
-std::string_view ToString(CloudProvider Provider);
-
 /** Snapshot of detected cloud instance properties. */
 struct CloudInstanceInfo
 {
diff --git a/src/zencompute/include/zencompute/mockimds.h b/src/zencompute/include/zencompute/mockimds.h
index 521722e63..704306913 100644
--- a/src/zencompute/include/zencompute/mockimds.h
+++ b/src/zencompute/include/zencompute/mockimds.h
@@ -1,102 +1,6 @@
 // Copyright Epic Games, Inc. All Rights Reserved.
+// Moved to zenutil — this header is kept for backward compatibility.
 
 #pragma once
 
-#include <zencompute/cloudmetadata.h>
-#include <zenhttp/httpserver.h>
-
-#include <string>
-
-#if ZEN_WITH_TESTS
-
-namespace zen::compute {
-
-/**
- * Mock IMDS (Instance Metadata Service) for testing CloudMetadata.
- *
- * Implements an HttpService that responds to the same URL paths as the real
- * cloud provider metadata endpoints (AWS IMDSv2, Azure IMDS, GCP metadata).
- * Tests configure which provider is "active" and set the desired response
- * values, then pass the mock server's address as the ImdsEndpoint to the
- * CloudMetadata constructor.
- *
- * When a request arrives for a provider that is not the ActiveProvider, the
- * mock returns 404, causing CloudMetadata to write a sentinel file and move
- * on to the next provider — exactly like a failed probe on bare metal.
- *
- * All config fields are public and can be mutated between poll cycles to
- * simulate state changes (e.g. a spot interruption appearing mid-run).
- *
- * Usage:
- *   MockImdsService Mock;
- *   Mock.ActiveProvider = CloudProvider::AWS;
- *   Mock.Aws.InstanceId = "i-test";
- *   // ... stand up ASIO server, register Mock, create CloudMetadata with endpoint
- */
-class MockImdsService : public HttpService
-{
-public:
-	/** AWS IMDSv2 response configuration. */
-	struct AwsConfig
-	{
-		std::string Token			 = "mock-aws-token-v2";
-		std::string InstanceId		 = "i-0123456789abcdef0";
-		std::string AvailabilityZone = "us-east-1a";
-		std::string LifeCycle		 = "on-demand";	 // "spot" or "on-demand"
-
-		// Empty string → endpoint returns 404 (instance not in an ASG).
-		// Non-empty → returned as the response body. "InService" means healthy;
-		// anything else (e.g. "Terminated:Wait") triggers termination detection.
-		std::string AutoscalingState;
-
-		// Empty string → endpoint returns 404 (no spot interruption).
-		// Non-empty → returned as the response body, signalling a spot reclaim.
-		std::string SpotAction;
-	};
-
-	/** Azure IMDS response configuration. */
-	struct AzureConfig
-	{
-		std::string VmId	 = "vm-12345678-1234-1234-1234-123456789abc";
-		std::string Location = "eastus";
-		std::string Priority = "Regular";  // "Spot" or "Regular"
-
-		// Empty → instance is not in a VM Scale Set (no autoscaling).
-		std::string VmScaleSetName;
-
-		// Empty → no scheduled events. Set to "Preempt", "Terminate", or
-		// "Reboot" to simulate a termination-class event.
-		std::string ScheduledEventType;
-		std::string ScheduledEventStatus = "Scheduled";
-	};
-
-	/** GCP metadata response configuration. */
-	struct GcpConfig
-	{
-		std::string InstanceId		 = "1234567890123456789";
-		std::string Zone			 = "projects/123456/zones/us-central1-a";
-		std::string Preemptible		 = "FALSE";	 // "TRUE" or "FALSE"
-		std::string MaintenanceEvent = "NONE";	 // "NONE" or event description
-	};
-
-	/** Which provider's endpoints respond successfully.
-	 *  Requests targeting other providers receive 404.
-	 */
-	CloudProvider ActiveProvider = CloudProvider::None;
-
-	AwsConfig	Aws;
-	AzureConfig Azure;
-	GcpConfig	Gcp;
-
-	const char* BaseUri() const override;
-	void		HandleRequest(HttpServerRequest& Request) override;
-
-private:
-	void HandleAwsRequest(HttpServerRequest& Request);
-	void HandleAzureRequest(HttpServerRequest& Request);
-	void HandleGcpRequest(HttpServerRequest& Request);
-};
-
-}  // namespace zen::compute
-
-#endif	// ZEN_WITH_TESTS
+#include <zenutil/cloud/mockimds.h>