You may use the HTML code below to make a button which will redirect your user to WMSPanel and log him in:
<form accept-charset="UTF-8" action="http://stats.test.com/account/login" method="post">
<input id="email" name="email" type="hidden" value="user@email.com" />
<input id="pass" name="pass" type="hidden" value="secret" />
<input class='submit' type='submit' value='Login to WMSPanel'>
</form>
Here, "user@email.com" is his login and "secret" is his password which you know as an account administrator.