Custom Credential Provider - How to enter password only once over RDP?

Question

When using Custom Credential Provider, you must enter the password 2 times. How to enter a password once and then the OTP code?

I know the documentation says it's not possible, but I've seen a working example. I have looked at several threads on stackoverflow:

• Windows Credential Provider - Change User name Label on new Tile
• Remote Desktop Connection with Custom Credential Provider

I tried to merge the code from the second branch with this code, but it didn't work.