Fairtrade_redirect.php

<?php
function hip_auto_login() {
	/* emails with + will not work "properly", then wont be logged in with this filter */
    if( isset( $_GET['u'] ) && isset( $_GET['plux'] ) && isset( $_GET['post_id'] ) ) {

        $email = wp_kses( $_GET['u'],array() );
        $checksum  = wp_kses( $_GET['plux'],array() );
    	$post_id = wp_kses( $_GET['post_id'],array() );

        if (!is_user_logged_in() && !empty($checksum) && !empty($email)) {

           // get sha256 checksum and salt it with AUTH_KEY constant defined in wp-config.php
           $real_checksum = hash('sha256', $email . AUTH_KEY);

           if (!empty($email) && $real_checksum == $checksum ) {
                    //login
                    $user = get_user_by('email', $email);
                    $userobject =  wp_set_current_user($user->ID, $email);
                    wp_set_auth_cookie($userobject->ID);
                    do_action('wp_login', $user->user_login);

    				$settings = (array) get_option( 'ft-schools-settings' );
    				$welcome_page = esc_attr( $settings['login-landing-page'] );
                    if( $welcome_page == "profile" ) $welcome_page = $post_id;
    				$redirect_to = get_permalink( $welcome_page );
                    header('Location: ' . $redirect_to);
                    die;
                }
        }
    }
    else{
    	$settings = (array) get_option( 'ft-schools-settings' );
		$welcome_page = esc_attr( $settings['login-landing-page'] );
        if( $welcome_page == "profile" ) $welcome_page = $post_id;
		$redirect_to = get_permalink( $welcome_page );
        header('Location: ' . $redirect_to);
        die;
    }
}