Is your feature request related to a problem? Please describe.
If I want to use an existing certificate when creating a new Entra App Registration, I need to pass in a path to the PFX file. But the PFX file should not actually be necessary. Entra ID expects a public key (a .CER file) when uploading a certificate file. The Private key is used in other places, in the case of PnP PowerShell it's used when signing in, for example when referencing the thumbprint or the path to the PFX itself.

The problem with passing in the PFX in the Register-PnPEntraIdApp command is that I don't want to. I may have installed the PFX in my windows credential store and thrown away the key (not being able to export it for security purposes, for example.)

Describe the solution you'd like
I'd like to be able to pass in the .CER file as a certificate (and not specify the password). PnP should just upload the file as a certificate and be done with it.

So now I'm forced to run

Register-PnPEntraIDApp -ApplicationName "some-name" -Tenant "contoso.onmicrosoft.com" -CertificatePath ".\some-cert.pfx" -CertificatePassword (ConvertTo-SecureString -String "somepassword" -AsPlainText)

but I essentially want to run:

Register-PnPEntraIDApp -ApplicationName "some-name" -Tenant "contoso.onmicrosoft.com" -CertificatePath ".\some-cert.cer"