s3/iam: reuse one request id per request (#8538)

* request_id: add shared request middleware

* s3err: preserve request ids in responses and logs

* iam: reuse request ids in XML responses

* sts: reuse request ids in XML responses

* request_id: drop legacy header fallback

* request_id: use AWS-style request id format

* iam: fix AWS-compatible XML format for ErrorResponse and field ordering

- ErrorResponse uses bare <RequestId> at root level instead of
  <ResponseMetadata> wrapper, matching the AWS IAM error response spec
- Move CommonResponse to last field in success response structs so
  <ResponseMetadata> serializes after result elements
- Add randomness to request ID generation to avoid collisions
- Add tests for XML ordering and ErrorResponse format

* iam: remove duplicate error_response_test.go

Test is already covered by responses_test.go.

* address PR review comments

- Guard against typed nil pointers in SetResponseRequestID before
  interface assertion (CodeRabbit)
- Use regexp instead of strings.Index in test helpers for extracting
  request IDs (Gemini)

* request_id: prevent spoofing, fix nil-error branch, thread reqID to error writers

- Ensure() now always generates a server-side ID, ignoring client-sent
  x-amz-request-id headers to prevent request ID spoofing. Uses a
  private context key (contextKey{}) instead of the header string.
- writeIamErrorResponse in both iamapi and embedded IAM now accepts
  reqID as a parameter instead of calling Ensure() internally, ensuring
  a single request ID per request lifecycle.
- The nil-iamError branch in writeIamErrorResponse now writes a 500
  Internal Server Error response instead of returning silently.
- Updated tests to set request IDs via context (not headers) and added
  tests for spoofing prevention and context reuse.

* sts: add request-id consistency assertions to ActionInBody tests

* test: update admin test to expect server-generated request IDs

The test previously sent a client x-amz-request-id header and expected
it echoed back. Since Ensure() now ignores client headers to prevent
spoofing, update the test to verify the server returns a non-empty
server-generated request ID instead.

* iam: add generic WithRequestID helper alongside reflection-based fallback

Add WithRequestID[T] that uses generics to take the address of a value
type, satisfying the pointer receiver on SetRequestId without reflection.

The existing SetResponseRequestID is kept for the two call sites that
operate on interface{} (from large action switches where the concrete
type varies at runtime). Generics cannot replace reflection there since
Go cannot infer type parameters from interface{}.

* Remove reflection and generics from request ID setting

Call SetRequestId directly on concrete response types in each switch
branch before boxing into interface{}, eliminating the need for
WithRequestID (generics) and SetResponseRequestID (reflection).

* iam: return pointer responses in action dispatch

* Fix IAM error handling consistency and ensure request IDs on all responses

- UpdateUser/CreatePolicy error branches: use writeIamErrorResponse instead
  of s3err.WriteErrorResponse to preserve IAM formatting and request ID
- ExecuteAction: accept reqID parameter and generate one if empty, ensuring
  every response carries a RequestId regardless of caller

* Clean up inline policies on DeleteUser and UpdateUser rename

DeleteUser: remove InlinePolicies[userName] from policy storage before
removing the identity, so policies are not orphaned.

UpdateUser: move InlinePolicies[userName] to InlinePolicies[newUserName]
when renaming, so GetUserPolicy/DeleteUserPolicy work under the new name.

Both operations persist the updated policies and return an error if
the storage write fails, preventing partial state.

weed/iamapi/iamapi_test.go

@@ -17,6 +17,7 @@ import (
 	"github.com/seaweedfs/seaweedfs/weed/pb/iam_pb"
 	"github.com/seaweedfs/seaweedfs/weed/s3api"
 	"github.com/seaweedfs/seaweedfs/weed/s3api/policy_engine"
+	"github.com/seaweedfs/seaweedfs/weed/util/request_id"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -73,6 +74,21 @@ func TestListUsers(t *testing.T) {
 	assert.Equal(t, http.StatusOK, response.Code)
 }
 
+func TestListUsersRequestIdMatchesResponseHeader(t *testing.T) {
+	params := &iam.ListUsersInput{}
+	req, _ := iam.New(session.New()).ListUsersRequest(params)
+	_ = req.Build()
+
+	out := ListUsersResponse{}
+	response, err := executeRequest(req.HTTPRequest, out)
+	assert.Equal(t, nil, err)
+	assert.Equal(t, http.StatusOK, response.Code)
+
+	headerRequestID := response.Header().Get(request_id.AmzRequestIDHeader)
+	assert.NotEmpty(t, headerRequestID)
+	assert.Equal(t, headerRequestID, extractRequestID(response))
+}
+
 func TestListAccessKeys(t *testing.T) {
 	svc := iam.New(session.New())
 	params := &iam.ListAccessKeysInput{}
@@ -246,6 +262,7 @@ func TestPutUserPolicyError(t *testing.T) {
 	assert.Equal(t, expectedCode, code)
 	assert.Contains(t, response.Body.String(), "<RequestId>")
 	assert.NotContains(t, response.Body.String(), "<ResponseMetadata>")
+	assert.Equal(t, response.Header().Get(request_id.AmzRequestIDHeader), extractRequestID(response))
 }
 
 func extractErrorCodeAndMessage(response *httptest.ResponseRecorder) (string, string) {
@@ -257,6 +274,15 @@ func extractErrorCodeAndMessage(response *httptest.ResponseRecorder) (string, st
 	return code, message
 }
 
+func extractRequestID(response *httptest.ResponseRecorder) string {
+	re := regexp.MustCompile(`<RequestId>([^<]+)</RequestId>`)
+	matches := re.FindStringSubmatch(response.Body.String())
+	if len(matches) < 2 {
+		return ""
+	}
+	return matches[1]
+}
+
 func TestGetUserPolicy(t *testing.T) {
 	userName := aws.String("Test")
 	params := &iam.GetUserPolicyInput{UserName: userName, PolicyName: aws.String("S3-read-only-example-bucket")}