[keycloak-dev] creating JPA user storage provider difficult

[Bill Burke]

I wrote an JPA example for the new User Storage Provider SPI [1].  It 
was very difficult to figure out how to wire in JPA.  I'm going to take 
a guess that very very few users have actually tried to implement a 
JPA-based User Federation Provider.  They would have run into a ton of 
hurdles.

* Putting just a jar within the "providers/" directory is unusable.  JPA 
classes and other dependencies will not be visible.

* So, you have to craft a *CORRECT* module.xml file and know exactly 
which dependencies to bring in. [2]

* javax.persistence.Persistence.createEntityManagerFactory() did not 
work, so I had to call Hibernate APIs directly.  Not only that, but 
non-simple Hibernate APIs. [3]

* When configuring JPA I also had to know what classloader to use so 
that persistence.xml was visible.

* Had to use JpaKeycloakTransaction to enlist EntityManager with 
keycloak transactions.  This means using EJBs is out of the question.

This is unacceptable.  Keycloak is supposed to be simple and this is 
extremely difficult.  When Keycloak was an exploded WAR you could use 
every Java EE component type as you could just plop your extensions 
within META-INF/lib.  Classloading was simple as it was all the same 
classloader.

Going forward we need to write an actual deployer for Keycloak 
extensions that allow you to define Keycloak providers within EE jars, 
ears, etc.  Writing an extension to Keycloak should be as easy as 
writing a Java EE application.  Extension developers should be able to 
leverage the entire JBoss/Wildfly platform. Minimally, we also need to 
begin and commit/rollback a UserTransaction within a Keycloak request 
flow so that transaction EE and Spring component layers can function.

Finally, we should just remove the "providers/" directory as I don't 
think it is very usable for actual extension writing.  What I didn't try 
was adding all jars needed (Hibernate etc.) within the providers 
directory.  Would that have worked?


[1] 
https://github.com/patriot1burke/keycloak/tree/master/examples/providers/user-storage-jpa

[2] 
https://github.com/patriot1burke/keycloak/blob/master/examples/providers/user-storage-jpa/module.xml

[3] 
https://github.com/patriot1burke/keycloak/blob/master/examples/providers/user-storage-jpa/src/main/java/org/keycloak/examples/storage/user/ExampleUserStorageProviderFactory.java#L74