fix(s3): use URL-safe secret keys for dashboard users and service accounts (#8902)

* fix(s3): use URL-safe secret keys for admin dashboard users and service accounts

The dashboard's generateSecretKey() used base64.StdEncoding which produces
+, /, and = characters that break S3 signature authentication. Reuse the
IAM package's GenerateSecretAccessKey() which was already fixed in #7990.

Fixes #8898

* fix: handle error from GenerateSecretAccessKey instead of ignoring it

weed/admin/dash/user_management.go

@@ -3,13 +3,13 @@ package dash
 import (
 	"context"
 	"crypto/rand"
-	"encoding/base64"
 	"errors"
 	"fmt"
 	"strings"
 	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/credential"
+	"github.com/seaweedfs/seaweedfs/weed/iam"
 	"github.com/seaweedfs/seaweedfs/weed/pb/iam_pb"
 )
 
@@ -435,10 +435,13 @@ func generateAccessKey() string {
 }
 
 func generateSecretKey() string {
-	// Generate 40-character secret key (AWS standard)
-	b := make([]byte, 30) // 30 bytes = 40 characters in base64
-	rand.Read(b)
-	return base64.StdEncoding.EncodeToString(b)
+	// Use the IAM helper to generate URL-safe secret keys (no +, / characters)
+	// that won't break S3 signature authentication
+	key, err := iam.GenerateSecretAccessKey()
+	if err != nil {
+		panic(fmt.Sprintf("failed to generate secret key: %v", err))
+	}
+	return key
 }
 
 func generateAccountId() string {

weed/admin/dash/user_management_test.go

@@ -74,9 +74,16 @@ func TestGenerateSecretKey(t *testing.T) {
 	key1 := generateSecretKey()
 	key2 := generateSecretKey()
 
-	// Check length (base64 encoding of 30 bytes = 40 characters)
-	if len(key1) != 40 {
-		t.Errorf("Expected secret key length 40, got %d", len(key1))
+	// Check length (IAM standard secret key length)
+	if len(key1) != 42 {
+		t.Errorf("Expected secret key length 42, got %d", len(key1))
+	}
+
+	// Check that key contains only URL-safe characters (no +, /)
+	for _, c := range key1 {
+		if c == '+' || c == '/' || c == '=' {
+			t.Errorf("Secret key contains non-URL-safe character: %c", c)
+		}
 	}
 
 	// Check uniqueness