我们是这样解决的:

Use memcache on server, with open connection from other password server. Save to memcache the password (or even all the password.php file encrypted) plus the decrypt key. The web site, calls the memcache key holding the password file passphrase and decrypt in memory all the passwords. The password server send a new encrypted password file every 5 minutes. If you using encrypted password.php on your project, you put an audit, that check if this file was touched externally - or viewed. When this happens, you automatically can clean the memory, as well as close the server for access.

之前我们将DB user/pass存储在一个配置文件中，但后来进入了偏执模式——采用了深度防御策略。

如果您的应用程序被泄露，用户将拥有对您的配置文件的读访问权，因此黑客就有可能读取这些信息。配置文件也可能在版本控制中被捕获，或者在服务器中被复制。

我们已经切换到在Apache VirtualHost中设置的环境变量中存储user/pass。这个配置只能由根用户读取——希望您的Apache用户不是以根用户身份运行。

这样做的缺点是，现在密码在一个全局PHP变量中。

为了降低这种风险，我们有以下预防措施:

The password is encrypted. We extend the PDO class to include logic for decrypting the password. If someone reads the code where we establish a connection, it won't be obvious that the connection is being established with an encrypted password and not the password itself. The encrypted password is moved from the global variables into a private variable The application does this immediately to reduce the window that the value is available in the global space. phpinfo() is disabled. PHPInfo is an easy target to get an overview of everything, including environment variables.

最安全的方法是在PHP代码中完全不指定这些信息。

如果你使用Apache，这意味着在httpd.conf或虚拟主机文件中设置连接细节。如果你这样做，你可以不带参数地调用mysql_connect()，这意味着PHP永远不会输出你的信息。

这是你在这些文件中指定这些值的方法:

php_value mysql.default.user      myusername
php_value mysql.default.password  mypassword
php_value mysql.default.host      server

然后像这样打开mysql连接:

<?php
$db = mysqli_connect();

或者像这样:

<?php
$db = mysqli_connect(ini_get("mysql.default.user"),
                     ini_get("mysql.default.password"),
                     ini_get("mysql.default.host"));

将它们存储在web根目录外的一个文件中。

是否可以在存储凭据的同一文件中创建数据库连接。将凭据内联到connect语句中。

mysql_connect("localhost", "me", "mypass");

否则最好在connect语句之后取消设置凭据，因为不在内存中的凭据不能从内存中读取;)

include("/outside-webroot/db_settings.php");  
mysql_connect("localhost", $db_user, $db_pass);  
unset ($db_user, $db_pass);  

只是把它放在配置文件的某个地方是通常完成的方式。只要确保你:

禁止从网络外的任何服务器访问数据库， 注意不要意外地向用户显示密码(在错误消息中，或通过PHP文件意外地作为HTML提供，等等)。