【問題描述】：同一使用者在同一時間多次登入如果不能檢測出來，是危險的。因為，你無法知道是否有其他使用者在登入你的賬戶。如何禁止同一使用者多次登入呢？
【解決方案】
(1) 每次登入，身份認證成功後，重新產生一個session_id。
session_regenerate_id(); session_register ("username") ;
(2) 在使用者資料庫中開一個sessionid欄位，重新產生session_id後，都更新該欄位。
$sessionid = session_id(); $db = new PDO('sqlite:softToken.db'); $sql = "update userinfo set sessionid ='$sessionid' where username='$username' and passwd='$passwd';"; $query = $db->prepare($sql); $query->execute();
(3) 建立一個session儲存使用者名稱
$_SESSION["username"] = $username;
(4) 利用url重寫，傳遞session_id
$url = "main.php?sid=".session_id(); unset($db); echo "<font color=blue>登入成功,正在跳轉!</font>" ; header ("Location:$url");
(5) 在需要跳轉的頁面，起始處加入
main.php
<?php header('Content-type:text/html; charset=utf-8'); $sessionid = $_GET['sid']; session_id($sessionid); session_start (); $username = $_SESSION["username"]; $db = new PDO('sqlite:softToken.db'); $sql = "select * from userinfo where username='$username' and sessionid='$sessionid';"; $query = $db->prepare($sql); $query->execute(); $user = $query->fetch(PDO::FETCH_OBJ); if ($user->username == ""){ session_destroy(); echo "<script language='javascript' type='text/javascript'>" ; echo "window.location.href = 'index.html';" ; echo "</script>" ; exit () ; } ?> <html> <body> ...... </body> </html>
以上就是php有效防止同一帳號同一時間多次登入的解決方案，希望對大家解決同一帳號同一時間多次登入問題有所協助。
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