[[servlet-authentication-cached]]
= CachingUserDetailsService

Spring Security's `CachingUserDetailsService` implements xref:servlet/authentication/passwords/user-details-service.adoc#servlet-authentication-userdetailsservice[UserDetailsService] offering support for caching authentication.

`CachingUserDetailsService` provides caching support for `UserDetails` by delegating the authentication process to the provided `UserDetailsService`. The result is then stored in a `UserCache` to reduce computation in subsequent calls.

Utilize this class by defining a `@Bean` of it that encapsulates a concrete implementation of `UserDetailsService` and set a `UserCache` to cache authenticated `UserDetails`.

For example:

[source,java]
----
@Bean
public CachingUserDetailsService cachingUserDetailsService(UserDetailsService delegate, UserCache userCache) {
    CachingUserDetailsService service = new CachingUserDetailsService(delegate);
    service.setUserCache(userCache);
    return service;
}
----

However, a preferable approach would be to use `@Cacheable` in your `UserDetailsService.loadUserByUsername(String)` implementation to cache `UserDetails` by `username`, reducing boilerplate and setup, especially if you are already using cache in your application.

For example:

[source,java]
----
@Service
public class MyCustomUserDetailsImplementation implements UserDetailsService {

    @Override
    @Cacheable
    public UserDetails loadUserByUsername(String username) {
        // some logic here to get the actual user details
        return userDetails;
    }
}
----