Unable to add keyCredentials value to Azure App manifest

Question

I used the instructions from Performing app-only operations on SharePoint Online through Azure AD,when I had to modify the app manifest to :

>   "keyCredentials": [
>     {
>       "customKeyIdentifier": "<mybase64CertHash>",
>       "keyId": "<myKeyId>",
>       "type": "AsymmetricX509Cert",
>       "usage": "Verify",
>       "value":  "<mybase64Cert>"
>      }   ],

I didn't get any errors upon upload, but when I download the manifest I saw that keyCredentials value was null:

I tried to readd to the manifest the required value "MIIDPjCCAiqgAwIBAgIQ3td...KFgcGi" but this caused to error:

Failed to save manifest.Error details: KeyValueMustBeNull  

I tried to modify one character in keyId and save but got following error:

Error converting value <MyOriginalKey> to type 'System.Guid'  

How to store the value that i need in keyCredentials ?

Answer 1

I submitted a ticket to MS and their answer was that this value is stored in their DB but for security reasons is not shown in Manifest. The same would be for password for example.
Since the CSOM calls (original purpose of the app) work seems like the answer I recieved is correct.