import org.apache.catalina.realm.NullRealm; //导入依赖的package包/类
/**
 *
 * @param authentication
 * @return Authentication
 */
@Override
public Authentication authenticate(Authentication authentication) {
    Realm realm;
    Set<GrantedAuthority> auths = new HashSet<>();
    try {
        realm = getTomcatContextRealm();
        if(realm instanceof NullRealm) {
            throw new ProviderNotFoundException("No Realms configured for Jwala to Authenticate");
        }
        Principal principal = realm.authenticate(authentication.getName(),
                authentication.getCredentials().toString());
        if (principal == null) {
            throw new BadCredentialsException("Username or Password not found.");
        } else {
            if (principal instanceof GenericPrincipal) {
                String[] roles = ((GenericPrincipal) principal).getRoles();
                for (String role : roles) {
                    auths.add(new SimpleGrantedAuthority(role));
                }
            }
            GrantedAuthoritiesMapperImpl grantedAuthoritiesMapper = new GrantedAuthoritiesMapperImpl();
            return new UsernamePasswordAuthenticationToken(authentication.getName(),
                    authentication.getCredentials(), grantedAuthoritiesMapper.mapAuthorities(auths));
        }
    } catch (AttributeNotFoundException | InstanceNotFoundException | MBeanException | ReflectionException e) {
        LOGGER.error("Error getting realms", e);
        throw new ProviderNotFoundException(e.getMessage());
    }
}