If you need to auto login a user and redirect to the user's home URL or a default URL you can use this page. Save it as <MA_HOME>\overrides\web\modules\dashboards\web\autoLogin\index.html and modify it to your needs.

Direct your web browser to <Mango URL>/user-dashboards/autoLogin and you will be automatically logged in (if you are not already logged in.

<!DOCTYPE html>
<html lang="en">
    <meta charset="utf-8">
    <meta http-equiv="x-ua-compatible" content="ie=edge">
    <title>Auto login</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <p>Logging in..</p>

    <script src="/resources/require.js"></script>
    <script src="/resources/loaderConfig.js"></script>
    <script src="../js/loaderConfig.js"></script>

require(['angular', 'mango-3.3/maServices'], function(angular) {
    const servicesInjector = angular.injector(['maServices'], true);
    const User = servicesInjector.get('User');
    User.current().$promise.then(null, () => {
        return User.login({username: 'viewonlyuser', password: 'viewonly'}).$promise;
    }).then((user) => {
        window.location = user.homeUrl || '/dashboards/home';