Automatically log in a user in PHP with a known email address and password. For example if you want to register and sign in a user, you can create the user via management API with a random password and then use it to sign the user in.

auth0-register-login-example.php

<?php
require_once(__DIR__."/vendor/autoload.php"); // Load SDK via Composer

// Initialize SDK like below - read Auth0 documentation for more information
$httpHost = empty($_SERVER["HTTP_X_FORWARDED_HOST"]) ? $_SERVER['SERVER_NAME'] : $_SERVER["HTTP_X_FORWARDED_HOST"];
$auth0 = new \Auth0\SDK\Auth0([
    'domain' => $_ENV['AUTH0_DOMAIN'],
    'clientId' => $_ENV['AUTH0_CLIENT_ID'],
    'clientSecret' => $_ENV['AUTH0_CLIENT_SECRET'],
    'cookieSecret' => $_ENV['AUTH0_COOKIE_SECRET'],
    'cookieDomain' => $httpHost,
    'cookieSecure' => $httpProtocol=="https",
]);
$auth0_pw_connection = "Username-Password-Authentication";
if (isset($_ENV['AUTH0_MANAGEMENT_API_TOKEN'])) {
    $auth0->configuration()->setManagementToken($_ENV['AUTH0_MANAGEMENT_API_TOKEN']);
}

// Generate a password and create a user like below
$email = $_GET["email"];
$management = $auth0->management();
$pw = bin2hex(random_bytes(10));
$response = decode_management_response($management->users()->create("Username-Password-Authentication", [
    "email" => $email,
    "email_verified" => false,
    "password" => $pw,
    "verify_email" => true,
]));

// Maybe immediately send a password forgotten email to allow the user to change the password?
$auth0->authentication()->dbConnectionsChangePassword($email, "Username-Password-Authentication");

login_user($email, $pw);


// Actual method to silently log in
use Auth0\SDK\Utility\{HttpResponse};
function login_user($email, $password) {
    global $auth0, $auth0_pw_connection;

    $response = decode_management_response($auth0->authentication()->login($email, $password, $auth0_pw_connection));
    if(!array_key_exists("access_token", $response)) return false;

    $auth0->clear();
    $auth0->setIdToken($response['id_token']);
    $auth0->setAccessToken($response['access_token']);

    if (isset($response['scope'])) {
        $auth0->setAccessTokenScope(explode(' ', $response['scope']));
    }

    if (isset($response['refresh_token'])) {
        $auth0->setRefreshToken($response['refresh_token']);
    }

    if (isset($response['expires_in']) && is_numeric($response['expires_in'])) {
        $expiresIn = time() + (int) $response['expires_in'];
        $auth0->setAccessTokenExpiration($expiresIn);
    }

    if (null === $user || $auth0->configuration()->getQueryUserInfo()) {
        $response = $auth0->authentication()->userInfo($response['access_token']);

        if (HttpResponse::wasSuccessful($response)) {
            $user = HttpResponse::decodeContent($response);
        }
    }

    $auth0->configuration()->getTransientStorage()->purge();
    $auth0->setUser($user ?? []);

    return true;
}

// Helper to read SDK response
function decode_management_response($raw_response) {
    return json_decode($raw_response->getBody()->__toString(), true, 512, JSON_THROW_ON_ERROR);
}