> For the complete documentation index, see [llms.txt](https://docs.vida.id/identity-stack/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.vida.id/identity-stack/authentication/authentication-factors/biometric-device-selfie-id/integration-methods/selfie-id-api/api/api-reference/authentication.md).

# Authentication

Authentication using the Selfie ID API validates a user's identity by comparing their live facial input against the previously stored template. The process ensures secure and frictionless access, using initiation and completion APIs to handle session flow.