Send a newly registered user and activation link

activation.php

<?php // Do not include this line in functions.php

// Use below this line in functions.php

/**
 * Helper function containing settings.
 *
 * Edit the values accordingly, making sure to 
 * leave the array keys intact.
 */
function my_activation_key_settings() {
    $settings = array(
        'email_text'      => 'Click to activate your account: ',
        'return_url'      => 'http://yoursite.com/your-page/',
        'send_welcome'    => true,
        'show_success'    => true,
        'success_message' => 'Thank you for activating your account.',
        'send_notify'     => true,
    );  
    return $settings;
}

/*
 * While the following is editable as needed, if you just
 * want a plug-and-play solution, you can use everything
 * as-is without changing anything below this line.
 */

/**
 * Create an activation key for the
 * user at registration.
 */
add_action( 'wpmem_post_register_data', 'my_generate_key' );
function my_generate_key( $fields ) {
     
    // Generate a random key.
    $key = md5( wp_generate_password() );
     
    // Save this for the new user account.
    add_user_meta( $fields['ID'], 'activation_key', $key );
}

/**
 * Include the activation key in the new user
 * registration email as an activation link.
 */
add_filter( 'wpmem_email_filter', 'my_add_key_to_email', 10, 3 );
function my_add_key_to_email( $arr, $wpmem_fields, $field_data ) {
     
    $settings = my_activation_key_settings();
    $url = trailingslashit( $settings['return_url'] );
     
    // Only do this for new registrations.
    if ( $arr['toggle'] == 'newmod' ) {
        // Get the stored key.
        $key = get_user_meta( $arr['user_id'], 'activation_key', true );
        // Add text and link to the email body.
        $arr['body'] = $arr['body'] . "\r\n"
            . $settings['email_text']
            . add_query_arg( 'activate', $key, $url );
    }
     
    return $arr;
}

/**
 * Check for an activation key and if one exists,
 * validate and log in user.
 */
add_action( 'template_redirect', 'my_validate_key' );
function my_validate_key() {
     
    $settings = my_activation_key_settings();
     
    // Check for activation key.
    if ( isset( $_GET['activate'] ) ) {
         
        // Get the user account the key is for.
        $users = get_users( array(
            'meta_key'    => 'activation_key',
            'meta_value'  => $_GET['activate'],
            'number'      => 1,
            'count_total' => false
        ) );
         
        if ( $users ) {
            foreach( $users as $user ) {
                 
                // The provided activation key was valid, log in.
                wp_set_auth_cookie( $user->ID, true );
                wp_set_current_user( $user->ID );
 
                // Delete activation_key meta and set active.
                delete_user_meta( $user->ID, 'activation_key' );
                update_user_meta( $user->ID, 'active', '1' );
                 
                if ( $settings['send_welcome'] ) {
                    // Send a welcome email
                    include_once( WPMEM_PATH . 'inc/email.php' );
                    wpmem_inc_regemail( $user->ID, '', 2 );
                }
                 
                if ( $settings['send_notify'] ) {
                    // Send a welcome email
                    global $wpmem;
                    include_once( WPMEM_PATH . 'inc/email.php' );
                    wpmem_notify_admin( $user->ID, $wpmem->fields );
                }
                break;
            }
        }
    }
}

/**
 * Filters the content to show thank you message
 * on successful activation.
 */
add_filter( 'the_content', 'my_show_thankyou_on_activation', 100 );
function my_show_thankyou_on_activation( $content ) {
     
    $settings = my_activation_key_settings();
     
    if ( $settings['show_success'] && isset( $_GET['activate'] ) ) {
        // Load dependencies.
        include_once( WPMEM_PATH . 'inc/dialogs.php' );
        $content = wpmem_inc_regmessage( '', $settings['success_message'] ) . $content;
    }
     
    return $content;
}