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As I understand your issue here, you are not able to view the secret name of Azure key vault in ARM template JSON . Please let me know if my understanding is wrong.
It is the expected scenario. Key vault Secret names will not be visible in the ARM template.
As per the Best practices for CI/CD , While using Key vault in CICD process, it is recommended to keep the same secret names across all stages. If you keep the same secret names, you don't need to parameterize each connection string across CI/CD environments because the only thing that changes is the key vault name
When you use linked services whose connection information is stored in Azure Key Vault, it is recommended to keep separate key vaults for different environments. You can also configure separate permission levels for each key vault. For example, you might not want your team members to have permissions to production secrets. If you follow this approach, we recommend that you to keep the same secret names across all stages. If you keep the same secret names, you don't need to parameterize each connection string across CI/CD environments because the only thing that changes is the key vault name, which is a separate parameter.
Please let us know if the suggested response helped. Thanks!