Correction LDAP validation (#342)

* Correction LDAP username validation

As https://msdn.microsoft.com/en-us/library/aa366101(v=vs.85).aspx describe spaces should not be in start or at the end of username but they can be inside the username. So please check my solution for it.

* Check for zero length passwords in LDAP module.

According to https://tools.ietf.org/search/rfc4513#section-5.1.2 LDAP client should always check before bind whether a password is an empty value. There are at least one LDAP implementation which does not return error if you try to bind with DN set and empty password - AD.

* Clearing the login/email spaces at the [start/end]

models/login_source.go

@@ -548,9 +548,9 @@ func ExternalUserLogin(user *User, login, password string, source *LoginSource,
 func UserSignIn(username, password string) (*User, error) {
 	var user *User
 	if strings.Contains(username, "@") {
-		user = &User{Email: strings.ToLower(username)}
+		user = &User{Email: strings.ToLower(strings.TrimSpace(username))}
 	} else {
-		user = &User{LowerName: strings.ToLower(username)}
+		user = &User{LowerName: strings.ToLower(strings.TrimSpace(username))}
 	}
 
 	hasUser, err := x.Get(user)

modules/auth/ldap/ldap.go

@@ -151,6 +151,11 @@ func bindUser(l *ldap.Conn, userDN, passwd string) error {
 
 // SearchEntry : search an LDAP source if an entry (name, passwd) is valid and in the specific filter
 func (ls *Source) SearchEntry(name, passwd string, directBind bool) (string, string, string, string, bool, bool) {
+	// See https://tools.ietf.org/search/rfc4513#section-5.1.2
+	if len(passwd) == 0 {
+		log.Debug("Auth. failed for %s, password cannot be empty")
+		return "", "", "", "", false, false
+	}
 	l, err := dial(ls)
 	if err != nil {
 		log.Error(4, "LDAP Connect error, %s:%v", ls.Host, err)