Implement IAM propagation to S3 servers (#8130)

* Implement IAM propagation to S3 servers

- Add PropagatingCredentialStore to propagate IAM changes to S3 servers via gRPC
- Add Policy management RPCs to S3 proto and S3ApiServer
- Update CredentialManager to use PropagatingCredentialStore when MasterClient is available
- Wire FilerServer to enable propagation

* Implement parallel IAM propagation and fix S3 cluster registration

- Parallelized IAM change propagation with 10s timeout.
- Refined context usage in PropagatingCredentialStore.
- Added S3Type support to cluster node management.
- Enabled S3 servers to register with gRPC address to the master.
- Ensured IAM configuration reload after policy updates via gRPC.

* Optimize IAM propagation with direct in-memory cache updates

* Secure IAM propagation: Use metadata to skip persistence only on propagation

* pb: refactor IAM and S3 services for unidirectional IAM propagation

- Move SeaweedS3IamCache service from iam.proto to s3.proto.
- Remove legacy IAM management RPCs and empty SeaweedS3 service from s3.proto.
- Enforce that S3 servers only use the synchronization interface.

* pb: regenerate Go code for IAM and S3 services

Updated generated code following the proto refactoring of IAM synchronization services.

* s3api: implement read-only mode for Embedded IAM API

- Add readOnly flag to EmbeddedIamApi to reject write operations via HTTP.
- Enable read-only mode by default in S3ApiServer.
- Handle AccessDenied error in writeIamErrorResponse.
- Embed SeaweedS3IamCacheServer in S3ApiServer.

* credential: refactor PropagatingCredentialStore for unidirectional IAM flow

- Update to use s3_pb.SeaweedS3IamCacheClient for propagation to S3 servers.
- Propagate full Identity object via PutIdentity for consistency.
- Remove redundant propagation of specific user/account/policy management RPCs.
- Add timeout context for propagation calls.

* s3api: implement SeaweedS3IamCacheServer for unidirectional sync

- Update S3ApiServer to implement the cache synchronization gRPC interface.
- Methods (PutIdentity, RemoveIdentity, etc.) now perform direct in-memory cache updates.
- Register SeaweedS3IamCacheServer in command/s3.go.
- Remove registration for the legacy and now empty SeaweedS3 service.

* s3api: update tests for read-only IAM and propagation

- Added TestEmbeddedIamReadOnly to verify rejection of write operations in read-only mode.
- Update test setup to pass readOnly=false to NewEmbeddedIamApi in routing tests.
- Updated EmbeddedIamApiForTest helper with read-only checks matching production behavior.

* s3api: add back temporary debug logs for IAM updates

Log IAM updates received via:
- gRPC propagation (PutIdentity, PutPolicy, etc.)
- Metadata configuration reloads (LoadS3ApiConfigurationFromCredentialManager)
- Core identity management (UpsertIdentity, RemoveIdentity)

* IAM: finalize propagation fix with reduced logging and clarified architecture

* Allow configuring IAM read-only mode for S3 server integration tests

* s3api: add defensive validation to UpsertIdentity

* s3api: fix log message to reference correct IAM read-only flag

* test/s3/iam: ensure WaitForS3Service checks for IAM write permissions

* test: enable writable IAM in Makefile for integration tests

* IAM: add GetPolicy/ListPolicies RPCs to s3.proto

* S3: add GetBucketPolicy and ListBucketPolicies helpers

* S3: support storing generic IAM policies in IdentityAccessManagement

* S3: implement IAM policy RPCs using IdentityAccessManagement

* IAM: fix stale user identity on rename propagation

test/s3/iam/s3_iam_framework.go

@@ -810,7 +810,7 @@ func (f *S3IAMTestFramework) Cleanup() {
 	}
 }
 
-// WaitForS3Service waits for the S3 service to be available
+// WaitForS3Service waits for the S3 service to be available and checks for IAM write permissions
 func (f *S3IAMTestFramework) WaitForS3Service() error {
 	// Create a basic S3 client
 	sess, err := session.NewSession(&aws.Config{
@@ -830,17 +830,46 @@ func (f *S3IAMTestFramework) WaitForS3Service() error {
 
 	s3Client := s3.New(sess)
 
-	// Try to list buckets to check if service is available
+	// Create IAM client for write permission check
+	iamClient := iam.New(sess)
+
+	// Try to list buckets to check if S3 service is available
 	maxRetries := 30
 	for i := 0; i < maxRetries; i++ {
 		_, err := s3Client.ListBuckets(&s3.ListBucketsInput{})
 		if err == nil {
+			// S3 is up, now check if IAM is writable
+			// We try to create a dummy user. If it fails with "AccessDenied: IAM write operations are disabled",
+			// we know we are still in read-only mode (or the flag didn't take effect).
+			// If it fails with other errors (e.g. invalid auth), that's fine for this connectivity check.
+			// Only the explicit read-only error is a blocker for our specific test scenario.
+
+			// Note: We use a random name to avoid conflicts if it actually succeeds
+			dummyUser := fmt.Sprintf("check-writable-%d", time.Now().UnixNano())
+			_, iamErr := iamClient.CreateUser(&iam.CreateUserInput{
+				UserName: aws.String(dummyUser),
+			})
+
+			if iamErr != nil {
+				if reqErr, ok := iamErr.(awserr.RequestFailure); ok {
+					if reqErr.Code() == "AccessDenied" && strings.Contains(reqErr.Message(), "IAM write operations are disabled") {
+						f.t.Logf("Waiting for IAM to become writable... (attempt %d/%d)", i+1, maxRetries)
+						time.Sleep(1 * time.Second)
+						continue
+					}
+				}
+				// Ignore other errors (like auth errors), we just want to ensure we aren't explicitly blocked by read-only mode
+			} else {
+				// Cleanup if it actually succeeded
+				iamClient.DeleteUser(&iam.DeleteUserInput{UserName: aws.String(dummyUser)})
+			}
+
 			return nil
 		}
 		time.Sleep(1 * time.Second)
 	}
 
-	return fmt.Errorf("S3 service not available after %d retries", maxRetries)
+	return fmt.Errorf("S3 service not available or not writable after %d retries", maxRetries)
 }
 
 // PutTestObject puts a test object in the specified bucket