keycloak-scim/topics/user-storage/migration.adoc

=== Migratring from Old User Federation SPI

NOTE:  You do not need to read this chapter if you have not implemented a provider using the old (and removed)
       User Federation SPI

Keycloak had an older User Federation SPI in Keycloak 2.4.0 and earlier.  RH-SSO 7.0, although unsupported, also had
this older SPI available as well.  This older User Federation SPI has been removed in Keycloak 2.5.0 and RH-SSO 7.1.
If you have written a provider with this older SPI, this chapter discusses some strategies you can use to port it.


==== Import vs. Non-Import

The old User Federation SPI required you to create a local copy of a user in the {{book.project.name}}'s database
and import information from your exteral store to the local copy.  This is no longer a requirement.  You can still
port your old provider as-is, but you should consider whether a non-import strategy might be a better approach.

Advantages of Import Strategy:

* {{book.project.name}} basically becomes a persistence user cache for your external store.  Once the user is imported
you'll no longer hit the external store thus taking load off of it.
* If you are moving to {{book.project.name}} as your official user store and deprecating the old external store, you
can slowly migrate applications to use {{book.project.name}}.  When all applications have been migrated, unlink the
imported user, and retire the old legacy external store.

There are some obvious disadvantages though to using an import strategy:

* Looking up a user for the first time will require multiple updates to {{book.project.name}} database.  This can
be a big performance loss under load and put a lot of strain on the {{book.project.name}} database.  The user federated
storage approach will only store extra data as needed and may never be used depending on the capabilities of your external store.
* With the import approach, you have to keep local keycloak storage and external storage in sync.  The User Storage SPI
has capability interfaces that you can implement to support synchronization, but this can quickly become painful and messy.

==== UserFederationProvider vs. UserStorageProvider

The first thing to notice is that `UserFederationProvider` was a complete interface.  You just implemented every method
in this interface.  `UserStorageProvider` instead has broken up this interface into multiple capability interfaces that
you implement as needed.

`UserFederationProvider.getUserByUsername()` and `getUserByEmail()` have exact equivalents in the new SPI.  The difference
between the two is how you import.  If you are going to continue with an import strategy, you no longer call
`KeycloakSession.userStorage().addUser()' to create the user locally.  Instead you call `KeycloakSession.userLocalStorage().addUser()`.
The `userStorage()` method no longer exists.

The `UserFederationProvider.validateAndProxy()` method has been moved to an optional capability interface, `ImportedUserValidation`.
You'll want to implement this interface if you are porting your old provider as-is.
Also note that in the old SPI, this method was called every time the user was accessed, even if the local user is in the cache.
In the new SPI, this method is only called when the local user is loaded from local storage.  If the local user is cached,
then the `ImportedUserValidation.validate()` method is not called at all.

The `UserFederationProvider.isValid()` method no longer exists in the new model.

The `UserFederationProvider` methods `synchronizeRegistrations()`, `registerUser()`, and `removeUser()` methods have been
moved to the `UserRegistrationProvider` capability interface.  This new interface is optional to implement so if your
provider does not support creating and removing users, you don't have to implement it.  If your old provider had switch
to toggle support for registering new users, this would be supported in the new SPI be returning `null` from
`UserRegistrationProvider.addUser()` if the provider doesn't support adding users.

The older `UserFederationProvider` methods centered around credentials are now encapsulated in the `CredentialInputValidator`
and `CredentialInputUpdater` interfaces, which are also optional to implement depending on if you support validating or
updating credentials.  Credential management used to exist in `UserModel` methods.  These also have been moved to the
`CredentialInputValidator` and `CredentialInputUpdater` interfaces.
One thing to note that if you do not implement the `CredentialInputUpdater` interface, then
any credentials provided by your provider may be overridden locally in {{book.project.name}} storage.  So if you want
your credentials to be read-only, you should implement the `CredentialInputUpdater.updateCredential()` method and
return a `ReadOnlyException`.

The `UserFederationProvider` query methods like `searchByAttributes()` and `getGroupMembers()` are now encapsulated
in an optional interface `UserQueryProvider`.  If you do not implement this interface, then users will not be viewable
in the admin console.  You'll still be able to login though.

==== UserFederationProviderFactory vs. UserStorageProviderFactory

The synchronization methods in the old SPI are now encapsulated within an optional `ImportSynchronization` interface.
If you have implemented synchronization logic, then have your new `UserStorageProviderFactory` implement the
`ImportSynchronization` interface.

==== Upgrading to new Model

The User Storage SPI instances are stored in a completely different set of relational tables or Mongo schema.  {{book.project.name}}
automatically runs a migration script.  If any older User Federation providers are deployed for a realm, they will be converted
to the new storage model as is, including the `id` of the data.  This migration will only happen if there exists a User Storage provider
with the same provider id (i.e. "ldap", "kerberos") as the old User Federation provider.

So, knowing this there are different approaches you can take.

. You can remove the old provider in your old {{book.project.name}} deployment.  This will remove all local linked copies
  of imported users.  Then, when you upgrade {{book.project.name}}, just deploy and configure your new provider for your realm.
. The second option is to write your new provider making sure it has the same provider id: `UserStorageProviderFactory.getId()`.
  Make sure this provider is in the `deploy/` directory of the new {{book.project.name}} installation.  Boot the server, and have
  the built-in migration script convert from the old data model to the new data model.  In this case all your old linked imported
  users will work and be the same.

If you have decided to get rid of the import strategy and rewrite your User Storage provider, we suggest that you remove the old provider
before upgrading {{book.project.name}}.  This will remove linked local imported copies of any user you imported.