What is the "certpassword" used in winhttpcertcfg?
The certpassword is the passphrase you created during pem to .p12 conversion.
For Microsoft.NET 1.1 environments, you must convert pem-formatted API Certificates to .p12 format. The pem format is the format the Certificate is in when you download it from PayPal.
Once you download the pem file, use OpenSSL to convert it to .p12 format for use within your application. As part of this OpenSSL conversion process, you have to enter a passphrase. This passphrase is the "certpassword" used in the winhttpcertcfg command.
For Microsoft ASP.NET Web applications, you must use the winhttpcertcfg utility to "install" the .p12 certificate into your system keystore. The winhttpcertcfg command to use is:
WinHttpCertCfg -i certfile.p12 -p certpassword -c LOCAL_MACHINE\my -a username
The certpassword is the password you supplied during the pem to .p12 conversion using OpenSSL. Don't confuse this with your API account password.
When you first request an API Certificate, you're automatically assigned an API account name and you choose your own API account password.
Note: You can set the API account password to be the same as the certpassword you used to convert the pem file to .p12 format, but the two don't have to be the same.