Add SFTP Server Support (#6753)

* Add SFTP Server Support

Signed-off-by: Mohamed Sekour <mohamed.sekour@exfo.com>

* fix s3 tests and helm lint

Signed-off-by: Mohamed Sekour <mohamed.sekour@exfo.com>

* increase  helm chart version

* adjust version

---------

Signed-off-by: Mohamed Sekour <mohamed.sekour@exfo.com>
Co-authored-by: chrislu <chris.lu@gmail.com>

weed/sftpd/auth/password.go

@@ -0,0 +1,64 @@
+package auth
+
+import (
+	"fmt"
+	"math/rand"
+	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/sftpd/user"
+	"golang.org/x/crypto/ssh"
+)
+
+// PasswordAuthenticator handles password-based authentication
+type PasswordAuthenticator struct {
+	userStore user.Store
+	enabled   bool
+}
+
+// NewPasswordAuthenticator creates a new password authenticator
+func NewPasswordAuthenticator(userStore user.Store, enabled bool) *PasswordAuthenticator {
+	return &PasswordAuthenticator{
+		userStore: userStore,
+		enabled:   enabled,
+	}
+}
+
+// Enabled returns whether password authentication is enabled
+func (a *PasswordAuthenticator) Enabled() bool {
+	return a.enabled
+}
+
+// Authenticate validates a password for a user
+func (a *PasswordAuthenticator) Authenticate(conn ssh.ConnMetadata, password []byte) (*ssh.Permissions, error) {
+	username := conn.User()
+
+	// Check if password auth is enabled
+	if !a.enabled {
+		return nil, fmt.Errorf("password authentication disabled")
+	}
+
+	// Validate password against user store
+	if a.userStore.ValidatePassword(username, password) {
+		return &ssh.Permissions{
+			Extensions: map[string]string{
+				"username": username,
+			},
+		}, nil
+	}
+
+	// Add delay to prevent brute force attacks
+	time.Sleep(time.Duration(100+rand.Intn(100)) * time.Millisecond)
+
+	return nil, fmt.Errorf("authentication failed")
+}
+
+// ValidatePassword checks if the provided password is valid for the user
+func ValidatePassword(store user.Store, username string, password []byte) bool {
+	user, err := store.GetUser(username)
+	if err != nil {
+		return false
+	}
+
+	// Compare plaintext password
+	return string(password) == user.Password
+}