UserDetailsService provides a single method that can be integrated with any of your authentication credential data stores:

public interface UserDetailsService {
    UserDetails loadUserByUsername(String username)
    throws UsernameNotFoundException;
}

loadUserByUsername should return UserDetails. The details of the UserDetails interface are as follows:

public interface UserDetails extends Serializable {
    Collection << ? extends GrantedAuthority > getAuthorities();
    String getPassword();
    String getUsername();
    boolean isAccountNonExpired();
    boolean isAccountNonLocked();
    boolean isCredentialsNonExpired();
    boolean isEnabled();
}

Spring Security also provides a default UserDetailsService service to talk to a relational database. It assumes a default schema. Two tables need to be created, adhering to a specific structure—users and authorities:

public class JdbcDaoImpl extends JdbcDaoSupport
implements UserDetailsService, MessageSourceAware {
    public static final String DEF_USERS_BY_USERNAME_QUERY
        = "select username,password,enabled " +
        "from users " + "where username = ?";
    public static final String DEF_AUTHORITIES_BY_USERNAME_QUERY
        = "select username,authority " +
        "from authorities " + "where username = ?";
    public static final String DEF_GROUP_AUTHORITIES_BY_USERNAME_QUERY
        = "select g.id, g.group_name, ga.authority " +
        "from groups g, group_members gm, group_authorities ga " +
        "where gm.username = ? " + "and g.id = ga.group_id " +
        "and g.id = gm.group_id";
}

You can also provide your own custom queries using the set methods in JdbcDaoImpl:

public void setAuthoritiesByUsernameQuery(String queryString)
public void setGroupAuthoritiesByUsernameQuery(String queryString)
public void setUsersByUsernameQuery(String usersByUsernameQueryString)