Cotter - One-click phone number login and checkout
Byepass - Eliminating passwords
Amazon Cognito - Amazon Cognito lets you add user sign-up, sign-in, and access control to your web and mobile apps quickly and easily. It scales to millions of users and supports sign-in with social identity providers and enterprise identity providers via SAML 2.0.
MojoAuth - Allow users to login without passwords
SuperTokens - Open Source User Authentication - An Alternative to Auth0 / Firebase Auth / AWS Cognito
One Account - Authentication always has been security or convenience, but why compromise?