How to obtain a private key for "Developer ID Application" or "Developer ID Installer" certificates?

Question

I'd like to understand how to obtain a private key for Developer ID Application or Developer ID Installer certificates?

1. Developer ID certificates may be created only by Account Holder https://developer.apple.com/support/roles/ - done
2. I have Developer ID Application certificate.
3. But there is missing private key.

Where may I find the appropriate private key?

Answer 1

To share Developer ID certificates the person who is Account Holder should:

1. Crete Developer ID certificate on developer account https://developer.apple.com/
2. Import it to keychain
3. Export certificate together with private key as p12 file
4. Share to developer p12 file with password

Answer 2

Ask the person who created this certificate to export the certificate and send it to you. Or any other existing developer who is already using this certificate.

You can not download private keys from the apple developer portal.