<form action="http://mysite.tld/wp-login.php" method="post">
    <label for="username">Username</label>
    <input type="text" name="username" id="username" value=""/><br/>
    <label for="password">Password</label>
    <input type="password" name="password" id="password" value=""/><br/>
    <input type="submit" value="login"/>
</form>