[keycloak-dev] caching custom per-user objects

[Bill Burke]

I've run into a few places where I need to cache custom things per-user 
that are evicted along with the user.  I also need some fine grain 
control of things that get cached with a user.  Here are the scenarios

* UserStorageProvider SPI needs to cache something that doesn't fit with 
the current UserModel metadata

* Certain credential types like HOTP need to be updated per login.  We 
don't want to cache these things, and we do not want to evict users in 
the cache that use these credential types

* It should be possible to cache credentials that are validated by an 
external provider.  For example, password and LDAP.   JBoss has 
supported caching successfully validated credentials since forever.


I'm going to expose a new interface via KeycloakSession: UserCache

interface UserCache extends UserProvider {

    boolean isCached(UserModel user);

    void cacheWith(UserMode userl, Object key, Object value);

}


I'm also going to add a callback interface

interface OnUserCache {

    void cacheUser(RealmModel realm, UserModel user, Map cache);

}

I originally thought about having a ProviderEvent for OnUserCache, but 
this callback needs to be targeted to specific objects rather than 
everything.  i.e. a specific User Storage Provider rather than being 
sent to every storage provider.


Bill