Even if someone was able to get that info, your vault will still be secure because in order to access your Key Vault and view the contents inside, a user, app, or identity will need to be added to your Key Vault's management plane (RBAC), and data plane (access policies) to view anything within your vault.
Therefore, if a user has a TenantID they still won't have access to your AKV unless they have the credentials of a user, app, or identity that has the correct RBAC and access policies permissions.
For more info: Management plane and Azure RBAC Data plane and access policies
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