The javadoc:org.springframework.security.core.CredentialsContainer[] interface indicates that the implementing object contains sensitive data, and is used internally by Spring Security to erase the authentication credentials after a successful authentication.
This interface is implemented by most of Spring Security internal domain classes, like javadoc:org.springframework.security.core.userdetails.User[] and javadoc:org.springframework.security.authentication.UsernamePasswordAuthenticationToken[].
The `ProviderManager` manager checks whether the returned `Authentication` implements this interface.
If so, xref:servlet/authentication/architecture.adoc#servlet-authentication-providermanager-erasing-credentials[it calls the `eraseCredentials` method] to remove the credentials from the object.
If you want your custom authentication objects to have their credentials erased after authentication, you should ensure that the classes implement the `CredentialsContainer` interface.
Users who are writing their own `AuthenticationProvider` implementations should create and return an appropriate `Authentication` object there, minus any sensitive data, rather than using this interface.
