Link Data JPA / Hibernate entities not using id field

I would like to link 2 entities but using a column that is not a primary key (and not marked with @Id in the class file).

@Entity
class MediaLog(
    @Id
    var id: UUID = UUID.randomUUID()
    var caseSystemId: String,
    var articleSummary: String?,
    var totalArticleCount: Int,
    var resolvedAt: Instant? = null,
    var lastCheckPerformedAt: Instant? = null
)

@Entity
@Audited
class CustomerCase(
    @Id
    var id: UUID = UUID.randomUUID()
    var authAccountId: UUID,
    @Enumerated(EnumType.STRING)
    var status: CaseStatus,
    var caseSystemId: String? = null
)

The relationship is OneToOne and they should be linked using the caseSystemId. The MediaLog MUST have a valid CustomerCase to link to it, but a there might be situations where some CustomerCase doesn't have any MediaLog entries. And yes, the MediaLog is not audited while the CustomerCase is audited (but that's not a problem).

I've tried all the possible combications of using @OneToOne and @JoinColumn, and playing with properties of each annotation but can't get it to work. Any ideas?