shell: address missed review feedback for PR 3

- s3.iam.import: require -force flag for destructive IAM overwrite
- s3.config.show: add nil guard for resp.Configuration
- s3.user.provision: check if user exists before creating policy
- s3.user.provision: reject wildcard bucket names (* ?)

weed/shell/command_s3_config_show.go

@@ -48,6 +48,10 @@ func (c *commandS3ConfigShow) Do(args []string, commandEnv *CommandEnv, writer i
 			return err
 		}
 		cfg := resp.Configuration
+		if cfg == nil {
+			fmt.Fprintln(writer, "No S3 IAM configuration found.")
+			return nil
+		}
 
 		fmt.Fprintf(writer, "S3 IAM Configuration Summary\n")
 		fmt.Fprintf(writer, "============================\n\n")

weed/shell/command_s3_iam_import.go

@@ -28,12 +28,12 @@ func (c *commandS3IAMImport) Name() string {
 func (c *commandS3IAMImport) Help() string {
 	return `import S3 IAM configuration from a JSON file
 
-	s3.iam.import -file backup.json
+	s3.iam.import -file backup.json -force
 
 	Replaces the entire IAM configuration (users, credentials, policies,
 	service accounts, groups) with the contents of the file.
 
-	WARNING: This overwrites the current configuration.
+	Requires -force to confirm, since this overwrites the current configuration.
 `
 }
 
@@ -44,6 +44,7 @@ func (c *commandS3IAMImport) HasTag(CommandTag) bool {
 func (c *commandS3IAMImport) Do(args []string, commandEnv *CommandEnv, writer io.Writer) error {
 	f := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
 	file := f.String("file", "", "input JSON file")
+	force := f.Bool("force", false, "confirm overwrite of the entire IAM configuration")
 	if err := f.Parse(args); err != nil {
 		return err
 	}
@@ -51,6 +52,9 @@ func (c *commandS3IAMImport) Do(args []string, commandEnv *CommandEnv, writer io
 	if *file == "" {
 		return fmt.Errorf("-file is required")
 	}
+	if !*force {
+		return fmt.Errorf("this overwrites the entire IAM configuration; use -force to confirm")
+	}
 
 	data, err := os.ReadFile(*file)
 	if err != nil {

weed/shell/command_s3_user_provision.go

@@ -6,6 +6,7 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"strings"
 	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/iam"
@@ -68,6 +69,9 @@ func (c *commandS3UserProvision) Do(args []string, commandEnv *CommandEnv, write
 	if *bucket == "" {
 		return fmt.Errorf("-bucket is required")
 	}
+	if strings.ContainsAny(*bucket, "*?") {
+		return fmt.Errorf("-bucket must be a literal bucket name, not a wildcard pattern")
+	}
 	if *role == "" {
 		return fmt.Errorf("-role is required (readonly, readwrite, admin)")
 	}
@@ -119,6 +123,11 @@ func (c *commandS3UserProvision) Do(args []string, commandEnv *CommandEnv, write
 		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 		defer cancel()
 
+		// Step 0: Check if user already exists
+		if resp, getErr := client.GetUser(ctx, &iam_pb.GetUserRequest{Username: *name}); getErr == nil && resp.Identity != nil {
+			return fmt.Errorf("user %q already exists", *name)
+		}
+
 		// Step 1: Create policy
 		_, err := client.PutPolicy(ctx, &iam_pb.PutPolicyRequest{
 			Name:    policyName,