feat(iam): implement group inline policy actions (#8992)

* feat(iam): implement group inline policy actions

Add PutGroupPolicy, GetGroupPolicy, DeleteGroupPolicy, and
ListGroupPolicies to both embedded and standalone IAM servers.

The standalone IAM stores group inline policies in a new
GroupInlinePolicies field in the Policies JSON, mirroring the
existing user inline policy pattern. DeleteGroup now also checks
for inline policies before allowing deletion.

* fix: address review feedback for group inline policies

- Embedded IAM: return NotImplemented for group inline policies
  instead of silently succeeding as no-ops (Gemini + CodeRabbit)
- Standalone IAM: recompute member actions after PutGroupPolicy
  and DeleteGroupPolicy (Gemini)
- Add parameter validation for GroupName/PolicyName/PolicyDocument
  on PutGroupPolicy, DeleteGroupPolicy, ListGroupPolicies (Gemini)
- Add UserName validation for ListUserPolicies in standalone IAM
- Call cleanupGroupInlinePolicies from DeleteGroup (Gemini)
- Migrate GroupInlinePolicies on group rename in UpdateGroup (CodeRabbit)
- Fix integration test cleanup order (CodeRabbit)

* fix: persist recomputed actions and improve error handling

- Set changed=true for PutGroupPolicy/DeleteGroupPolicy in standalone
  IAM DoActions so recomputed member actions are persisted (Gemini critical)
- Make cleanupGroupInlinePolicies accept policies parameter to avoid
  redundant I/O, return error (Gemini)
- Make migrateGroupInlinePolicies return error, handle in caller (Gemini)

* fix: include group policies in action recomputation

Extend computeAllActionsForUser to also aggregate group inline
policies and group managed policies when s3cfg is provided.
Previously, group inline policies were stored but never reflected
in member Identity.Actions. (CodeRabbit critical)

* perf: use identity index in recomputeActionsForGroupMembers for O(N+M)

* fix: skip group inline policy integration test on embedded IAM

The embedded IAM returns NotImplemented for group inline policies.
Skip TestIAMGroupInlinePolicy when running against embedded mode
to avoid CI failures in the group integration test matrix.

test/s3/iam/s3_iam_group_test.go

@@ -778,6 +778,105 @@ func TestIAMGroupRawAPI(t *testing.T) {
 	})
 }
 
+// TestIAMGroupInlinePolicy tests group inline policy operations:
+// PutGroupPolicy, GetGroupPolicy, ListGroupPolicies, DeleteGroupPolicy
+func TestIAMGroupInlinePolicy(t *testing.T) {
+	framework := NewS3IAMTestFramework(t)
+	defer framework.Cleanup()
+
+	iamClient, err := framework.CreateIAMClientWithJWT("admin-user", "TestAdminRole")
+	require.NoError(t, err)
+
+	// Skip if running against embedded IAM (which returns NotImplemented for group inline policies)
+	_, probeErr := iamClient.ListGroupPolicies(&iam.ListGroupPoliciesInput{GroupName: aws.String("probe-group-inline-support")})
+	if probeErr != nil {
+		if awsErr, ok := probeErr.(awserr.Error); ok && awsErr.Code() == "NotImplemented" {
+			t.Skip("Skipping: group inline policies not supported in embedded IAM mode")
+		}
+	}
+	require.NoError(t, err)
+
+	groupName := "test-group-inline-policy"
+	policyName := "TestInlinePolicy"
+	_, err = iamClient.CreateGroup(&iam.CreateGroupInput{
+		GroupName: aws.String(groupName),
+	})
+	require.NoError(t, err)
+	defer func() {
+		// Clean up inline policies before deleting the group
+		iamClient.DeleteGroupPolicy(&iam.DeleteGroupPolicyInput{
+			GroupName:  aws.String(groupName),
+			PolicyName: aws.String(policyName),
+		})
+		iamClient.DeleteGroup(&iam.DeleteGroupInput{GroupName: aws.String(groupName)})
+	}()
+
+	t.Run("list_empty", func(t *testing.T) {
+		resp, err := iamClient.ListGroupPolicies(&iam.ListGroupPoliciesInput{
+			GroupName: aws.String(groupName),
+		})
+		require.NoError(t, err)
+		assert.Empty(t, resp.PolicyNames)
+		assert.False(t, *resp.IsTruncated)
+	})
+
+	policyDoc := `{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Action":"s3:GetObject","Resource":"arn:aws:s3:::test-bucket/*"}]}`
+
+	t.Run("put_group_policy", func(t *testing.T) {
+		_, err := iamClient.PutGroupPolicy(&iam.PutGroupPolicyInput{
+			GroupName:      aws.String(groupName),
+			PolicyName:     aws.String(policyName),
+			PolicyDocument: aws.String(policyDoc),
+		})
+		require.NoError(t, err)
+	})
+
+	t.Run("list_after_put", func(t *testing.T) {
+		resp, err := iamClient.ListGroupPolicies(&iam.ListGroupPoliciesInput{
+			GroupName: aws.String(groupName),
+		})
+		require.NoError(t, err)
+		assert.NotEmpty(t, resp.PolicyNames)
+	})
+
+	t.Run("get_group_policy", func(t *testing.T) {
+		resp, err := iamClient.GetGroupPolicy(&iam.GetGroupPolicyInput{
+			GroupName:  aws.String(groupName),
+			PolicyName: aws.String(policyName),
+		})
+		require.NoError(t, err)
+		assert.Equal(t, groupName, *resp.GroupName)
+		assert.Equal(t, policyName, *resp.PolicyName)
+		assert.Contains(t, *resp.PolicyDocument, "s3:GetObject")
+	})
+
+	t.Run("delete_group_policy", func(t *testing.T) {
+		_, err := iamClient.DeleteGroupPolicy(&iam.DeleteGroupPolicyInput{
+			GroupName:  aws.String(groupName),
+			PolicyName: aws.String(policyName),
+		})
+		require.NoError(t, err)
+	})
+
+	t.Run("list_after_delete", func(t *testing.T) {
+		resp, err := iamClient.ListGroupPolicies(&iam.ListGroupPoliciesInput{
+			GroupName: aws.String(groupName),
+		})
+		require.NoError(t, err)
+		assert.Empty(t, resp.PolicyNames)
+	})
+
+	t.Run("nonexistent_group", func(t *testing.T) {
+		_, err := iamClient.ListGroupPolicies(&iam.ListGroupPoliciesInput{
+			GroupName: aws.String("nonexistent-group-for-policies"),
+		})
+		require.Error(t, err)
+		awsErr, ok := err.(awserr.Error)
+		require.True(t, ok, "Expected AWS error type")
+		assert.Equal(t, iam.ErrCodeNoSuchEntityException, awsErr.Code())
+	})
+}
+
 // createS3Client creates an S3 client with static credentials
 func createS3Client(t *testing.T, accessKey, secretKey string) *s3.S3 {
 	sess, err := session.NewSession(&aws.Config{