[[_extensions]]

== Extending the Server

The {project_name} SPI framework offers the possibility to implement or override particular built-in providers. However {project_name}
also provides capabilities to extend it's core functionalities and domain. This includes possibilities to:

* Add custom REST endpoints to the {project_name} server
* Add your own custom SPI
* Add custom JPA entities to the {project_name} data model

[[_extensions_rest]]
=== Add custom REST endpoints

This is a very powerful extension, which allows you to deploy your own REST endpoints to the {project_name} server. It enables all kinds of extensions, for example
the possibility to trigger functionality on the {project_name} server, which is not available through the default set of built-in {project_name} REST endpoints.

To add a custom REST endpoint, you need to implement the `RealmResourceProviderFactory` and `RealmResourceProvider` interfaces. `RealmResourceProvider` has one important method:

[source,java]
----

Object getResource();

----

which allows you to return an object, which acts as a https://github.com/jax-rs[JAX-RS Resource]. For more details, see the Javadoc and our examples.
There is a very simple example in the example distribution in `providers/rest` and there is a more advanced example in `providers/domain-extension`,
which shows how to add an authenticated REST endpoint and other functionalities like <<_extensions_spi, Adding your own SPI>>
or <<_extensions_jpa,Extending datamodel with your own JPA entities>>.

For details on how to package and deploy a custom provider, refer to the <<_providers,Service Provider Interfaces>> chapter.

[[_extensions_spi]]
=== Add your own custom SPI

This is useful especially with the <<_extensions_rest,Custom REST endpoints>>. To add your own kind of SPI, you need to
implement the interface `org.keycloak.provider.Spi` and define the ID of your SPI and the `ProviderFactory` and `Provider` classes. That looks like this:

[source,java]
----
package org.keycloak.examples.domainextension.spi;

import ...

public class ExampleSpi implements Spi {

    @Override
    public boolean isInternal() {
        return false;
    }

    @Override
    public String getName() {
        return "example";
    }

    @Override
    public Class<? extends Provider> getProviderClass() {
        return ExampleService.class;
    }

    @Override
    @SuppressWarnings("rawtypes")
    public Class<? extends ProviderFactory> getProviderFactoryClass() {
        return ExampleServiceProviderFactory.class;
    }

}

----

Then you need to create the file `META-INF/services/org.keycloak.provider.Spi` and add the class of your SPI to it. For example:

[source]
----
org.keycloak.examples.domainextension.spi.ExampleSpi
----

The next step is to create the interfaces `ExampleServiceProviderFactory`, which extends from `ProviderFactory` and `ExampleService`, which extends from `Provider`.
The `ExampleService` will usually contain the business methods you need for your use case. Note that the `ExampleServiceProviderFactory` instance
is always scoped per application, however `ExampleService` is scoped per-request (or more accurately per `KeycloakSession` lifecycle).

Finally you need to implement your providers in the same manner as described in the <<_providers,Service Provider Interfaces>> chapter.

For more details, take a look at the example distribution at `providers/domain-extension`, which shows an Example SPI similar to the one above.

[[_extensions_jpa]]
=== Add custom JPA entities to the {project_name} data model

If the {project_name} data model does not exactly match your desired solution, or if you want to add some core functionality to {project_name},
or when you have your own REST endpoint, you might want to extend the {project_name} data model. We enable you to add your
own JPA entities to the {project_name} JPA `EntityManager` .

To add your own JPA entities, you need to implement `JpaEntityProviderFactory` and `JpaEntityProvider`. The `JpaEntityProvider`
allows you to return a list of your custom JPA entities and provide the location and id of the Liquibase changelog. An example implementation can look like this:

NOTE: This is an unsupported API, which means you can use it but there is no guarantee that it will not be removed or changed without warning.

[source,java]
----
public class ExampleJpaEntityProvider implements JpaEntityProvider {

    // List of your JPA entities.
    @Override
    public List<Class<?>> getEntities() {
        return Collections.<Class<?>>singletonList(Company.class);
    }

    // This is used to return the location of the Liquibase changelog file.
    // You can return null if you don't want Liquibase to create and update the DB schema.
    @Override
    public String getChangelogLocation() {
    	return "META-INF/example-changelog.xml";
    }

    // Helper method, which will be used internally by Liquibase.
    @Override
    public String getFactoryId() {
        return "sample";
    }

    ...
}
----

In the example above, we added a single JPA entity represented by class `Company`. In the code of your REST endpoint, you can then use something like
this to retrieve `EntityManager` and call DB operations on it.


[source,java]
----
EntityManager em = session.getProvider(JpaConnectionProvider.class).getEntityManager();
Company myCompany = em.find(Company.class, "123");
----

The methods `getChangelogLocation` and `getFactoryId` are important to support automatic updating of your entities by Liquibase. https://www.liquibase.org/[Liquibase]
is a framework for updating the database schema, which {project_name} internally uses to create the DB schema and update the DB schema among versions. You may need to use
it as well and create a changelog for your entities. Note that versioning of your own Liquibase changelog is independent
of {project_name} versions. In other words, when you update to a new {project_name} version, you are not forced to update your
schema at the same time. And vice versa, you can update your schema even without updating the {project_name} version. The Liquibase update
is always done at the server startup, so to trigger a DB update of your schema, you just need to add the new changeset to your Liquibase changelog file (in the example above
it's the file `META-INF/example-changelog.xml` which must be packed in same JAR as the JPA entities and `ExampleJpaEntityProvider`) and then restart server.
The DB schema will be automatically updated at startup.

For more details, take a look at the example distribution at example `providers/domain-extension`, which shows the `ExampleJpaEntityProvider` and `example-changelog.xml` described above.

NOTE: Don't forget to always backup your database before doing any changes in the Liquibase changelog and triggering a DB update.