When was the last time you tried to upload a certificate to the Azure Key Vault? At the time of writing, you can’t from the portal.
Good news, you can using PowerShell. Below will guide you how to upload a private key certificate to Azure Key Vault:
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| ### Log into Azure | |
| Add-AzureRmAccount | |
| $Subscription = (Get-AzureRmSubscription | Out-GridView –Title "Choose a Source & Target Subscription …" –PassThru) | |
| Select-AzureRmSubscription –SubscriptionId $Subscription.Id | |
| # Upload Certificate to Azure's Key Vault | |
| $securepfxpwd = ConvertTo-SecureString –String 'password' –AsPlainText –Force # Password for the private key PFX certificate | |
| $certificateName = 'My-Cert' | |
| $vaultName = 'MyVault' | |
| $cer = Import-AzureKeyVaultCertificate –VaultName $vaultName –Name $certificateName –FilePath 'C:\My-Cert.pfx' –Password $securepfxpwd |
https://gist.github.com/marckean/03e0cad669e77903fd4f48e756e06a81#file-uploadpfxazurekeyvalut-ps1
https://gist.github.com/marckean/03e0cad669e77903fd4f48e756e06a81#file-uploadpfxazurekeyvalut-ps1
Marc Kean 
Did you happen to notice if your PFX password still worked when trying to download the secret afterward? It doesn’t. They strip out the value after you upload it. The PFX Import manager will only accept a null value as valid, I lost a couple of nights trying to figure this out.