How to specify the Auth0 SSO connection in WordPress with PHP and skip the Auth0 Login Page.

wp-auth0.php

<?php
/**
 * Get a valid list of Auth0 Connection slugs.
 * use the `wpa0_sso_connection` filter to add or remove slugs.
 * 
 * @return Array                    Array of Auth0 Connection slugs.
 */
function wpa0_sso_connections() {
    $connections = array();
    return apply_filters( 'wpa0_sso_connections', $connections );
}

/**
 * Filters to detect a specific connection that will
 * redirect the user to immediately (instead of hitting
 * the Auth0 page)
 * 
 * @param String    $connection     The Auth0 Connection slug.
 * 
 * @return String                   Auth0 Connection slug.
 */
add_filter( 'auth0_get_auto_login_connection', 'wpa0_auto_login_filter' );
function wpa0_auto_login_filter($connection) {
    if (isset($_GET['connection']) && !empty($_GET['connection']) && in_array($_GET['connection'], array_keys(wpa0_sso_connections()))) {
        return $_GET['connection'];
    }
    return $connection;
}

/**
 * Returns `wp_login_url` with the provided, vqlid Auth0 Connection slug.
 * For use in templating or other filters.
 * @link https://developer.wordpress.org/reference/functions/wp_login_url/
 * 
 * @param String    $redirect       (Optional) Path to redirect to on log in. Default value: '' 
 * @param Bool      $force_reauth   (Optional) Whether to force reauthorization, even if a cookie is present. Default value: false
 * @param String    $connection     (Optional) The Auth0 Connection slug (e.g. google-oauth2, twitter )
 * 
 * @return String                   The login URL.
 */
function wpa0_sso_login_url( $connection = '', $redirect = '', $force_reauth = false ) {
    $login_url = wp_login_url( $redirect, $force_reauth );
    return apply_filters( 'wpa0_sso_login_url', (!empty($connection)) ? add_query_arg('connection', $connection, $login_url) : $login_url );
}