Okta - Enterprise-grade identity management for all your apps, users & devices
Keycloak - Open Source Identity and Access Management for modern Applications and Services.
Auth0 - Auth0 is a program for people to get authentication and authorization services for their own business use.
IdentityServer - An open-source, standards-compliant, and flexible OpenID Connect and OAuth 2.x framework for ASP.NET Core
OneLogin - On-demand SSO, directory integration, user provisioning and more
openiddict - OpenIddict aims at providing a versatile solution to implement an OpenID Connect server and token validation in any ASP.NET Core