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.
Stripe - Online payment processing for internet businesses. Stripe is a suite of payment APIs that powers commerce for online businesses of all sizes. Use Stripe’s payment platform to accept and process payments online for easy-to-use commerce solutions.
Authorizer - Authorizer is an open-source authentication and authorization solution for your applications.
TypingDNA Authenticator - 2FA codes in your browser, secured by the way you type
Open Collective - Recurring funding for groups.
Stripe Billing Customer Portal - Stripe-hosted page for customers to manage subscriptions