Question: I need a system that can handle high volumes of login requests and provide flexible deployment options for scalability.

If you're looking for a system that can handle a large number of login requests and offer flexible deployment options for scalability, LoginRadius is a good option. It's a full-featured user identity management platform that offers advanced login features like social login, phone login and passwordless login. The system is designed to handle high traffic with a 100% uptime guarantee and can handle up to 240,000 login requests per second at peak load. It offers flexible deployment options, including private cloud, private cloud (managed) and multi-tenant cloud options across multiple cloud platforms.

Another good option is Supabase, an open-source Firebase alternative that includes a Postgres database, user authentication, instant APIs and real-time data synchronization. It supports popular frameworks like Next.js, Svelte and Flutter, and comes with a built-in user management system and various templates for common use cases. Supabase offers a free tier with unlimited API requests, so it can be a good option for scaling.

For a full-stack user management solution, Clerk offers a suite of embeddable UI components, flexible APIs and admin dashboards. It supports multifactor authentication, advanced security and integrates with popular frameworks. Clerk supports multi-tenancy with features like custom roles and permissions, auto-join and organization UI components. The free plan supports up to 10,000 monthly active users and 100 monthly active orgs, so it's a good option for those who need to scale.

Last, Auth0 offers secure access control with features like Universal Login, Single Sign On, Multi-factor Authentication and customizable actions. It's highly flexible and scalable, with support for integration with over 30 SDKs and Quickstarts. Auth0 offers a free plan to get you started, so you can experiment and evaluate the service before moving to a paid plan.