What authentication method uses identity providers for user authentication in Vault?

The authentication method that utilizes identity providers for user authentication in Vault is OIDC (OpenID Connect). OIDC is built on top of the OAuth 2.0 protocol and allows Vault to delegate authentication to an external identity provider. This is accomplished by using tokens issued by these external providers, enabling users to authenticate securely without needing to manage credentials directly within Vault.

By implementing OIDC, organizations can seamlessly integrate existing user identities from identity providers such as Google, Microsoft, or custom OAuth 2.0 compliant services. This not only simplifies user management but also enhances security by leveraging features such as single sign-on (SSO) and multifactor authentication (MFA) provided by the identity provider.

In contrast, the other methods mentioned do not inherently leverage external identity providers for user authentication. Token-based authentication relies on a specific token that Vault issues for access. LDAP authentication is directly linked to a directory service and requires configuration of that service within Vault. AppRole authentication is primarily designed for machines or applications and relies on role introspection by Vault rather than external identity verification.