KeycloakUserManagementService's user cache does not support non request scope and throws an exception

[maarten-ritense]

Expected behavior

No exception should be thrown when using the KeycloakUserManagementService.findByUserIdentifier from a non request scope like @Async or @Scheduled annotated methods.

Current behavior

When you annotate a method with @Async or @Scheduled and it then make use of the KeycloakUserManagementService.findByUserIdentifier to lookup a user via its user identifier the exception below is thrown:

org.springframework.beans.factory.support.ScopeNotActiveException: Error creating bean with name 'scopedTarget.requestScopeUserCache': Scope 'request' is not active for the current thread; consider defining a scoped proxy for this bean if you intend to refer to it from a singleton

Possible solution (optional)

Switch to a cache mechanism which is not scope restricted. I came across the Caffeine Cache (https://github.com/ben-manes/caffeine | https://www.baeldung.com/spring-boot-caffeine-cache) which is a high-performance cache library for Java and also has support for TTL of items so maybe that is an interesting cache to switch over to.

Steps to reproduce

Example of a piece of code which fails a.t.m. due to this exception which is triggered when a task is activated which has an assignee or when a task is assigned:

import mu.KotlinLogging
import com.ritense.valtimo.contract.authentication.UserManagementService
import org.camunda.bpm.spring.boot.starter.event.TaskEvent
import org.springframework.scheduling.annotation.Async
import org.springframework.transaction.event.TransactionPhase
import org.springframework.transaction.event.TransactionalEventListener
import java.util.UUID

open class CamundaTaskAssignedEventListener(
    private val userManagementService: UserManagementService
) {

    @Async
    @TransactionalEventListener(
        condition = "#taskEvent.eventName == 'assignment' && #taskEvent.assignee != null",
        phase = TransactionPhase.AFTER_COMMIT
    )
    open fun onTaskEvent(taskEvent: TaskEvent) {
        logger.debug {
            "Triggered by assignment of CamundaTask(id=${taskEvent.id}, name=${taskEvent.name}) to ${taskEvent.assignee})"
        }
        logger.info {"""
            TaskAssignedEvent(
                taskId = taskEvent.taskDefinitionKey,
                taskName = taskEvent.name,
                assignee = findByUsername(taskEvent.assignee),
                processInstanceId = UUID.fromString(taskEvent.processInstanceId),
                taskInstanceId = UUID.fromString(taskEvent.id)
            ) triggered by assignment of CamundaTask(id=${taskEvent.id}, name=${taskEvent.name}) to ${taskEvent.assignee})""".trimIndent()
        }
    }

    fun findByUsername(username: String): String {
        logger.debug { "Trying to find e-mail for user '$username'" }
        return userManagementService.findByUserIdentifier(username)?.email
            ?: throw UserNotFoundException.forUsername(username)
    }

    companion object {
        private val logger = KotlinLogging.logger {}
    }
}