Firebase Authentication is a popular identity solution for developers using Google Cloud, particularly for mobile-first or early-stage applications. However, as applications grow and become more complex, developers often seek alternatives due to Firebase's limitations such as vendor lock-in, limited backend flexibility, and challenges in meeting compliance requirements like GDPR or HIPAA. Alternatives like Descope, Supabase, Keycloak, Amazon Cognito, and Microsoft Entra External ID offer more customization, cost control, and enterprise-grade features. Descope provides a modern IAM platform with flexible, no-code authentication flows and multi-tenant support, making it suitable for B2C and B2B SaaS apps. Supabase, an open-source Firebase alternative, offers a backend-as-a-service experience with Postgres database support. Keycloak allows for full control over the authentication stack with self-hosted deployments. Amazon Cognito integrates deeply with AWS services and supports flexible identity federation, while Microsoft Entra External ID is tailored for complex enterprise environments with advanced security and compliance features. Each alternative has unique strengths, catering to different technical requirements and organizational needs, making them viable options for developers looking beyond Firebase Authentication.