> For AI agents: [llms.txt](https://docs.trustedauth.com/llms.txt) provides a Markdown index of this documentation.

# Authentication API core concepts

Use this section to understand authentication flows, transaction details, risk evaluation, and API security.

## Topics in this section

[📄️Authentication overview Use this page to understand prerequisites, the three-call Authentication API lifecycle, and the supported authenticators before you start integrating. For complete operation details, see the Authentication API reference.](/api/auth-api/core-concepts/authentication-overview.md)

[📄️Transaction details and push messages Use this page when you need to attach transaction data to an Authentication API request or customize Soft Token SDK push notifications.](/api/auth-api/core-concepts/transaction-details-and-push-messages.md)

[📄️Risk and machine authentication Use this page to understand how risk evaluation and machine authentication affect Authentication API flows.](/api/auth-api/core-concepts/risk-based-authentication-and-machine-authentication.md)

[📄️Authentication and support Use this page when you need a quick reference for the Authentication API security scheme or support details.](/api/auth-api/core-concepts/authentication-and-support.md)