Spring Security - The Spring portfolio has many projects, including Spring Framework, Spring IO Platform, Spring Cloud, Spring Boot, Spring Data, Spring Security...
Okta - Enterprise-grade identity management for all your apps, users & devices
Auth0 - Auth0 is a program for people to get authentication and authorization services for their own business use.
JSON Web Token - JSON Web Tokens are an open, industry standard RFC 7519 method for representing claims securely between two parties.
OneLogin - On-demand SSO, directory integration, user provisioning and more
Firebase Authentication - Application and Data, Application Utilities, and User Management and Authentication