I have purchased an App Service Certificate from Azure, but I need to change the password of it to install it in an Application Gateway. What is the password of the certificate by default? How would I change it?
The default password of the App Service Certificate when exported as PFX is empty, but as you say you cannot import it to the Application Gateway as it needs a password (other services in Azure do too). In order to change it, you can run this commands with OpenSSL (download: https://wiki.openssl.org/index.php/Binaries):
Export the PFX and private key to .pem:
openssl pkcs12 -in .\old.pfx -out old.pem -nodes
Then create a new PFX:
openssl pkcs12 -export -out .\new.pfx -in old.pem
In Windows you can import it in your machine, mark the key as exportable when importing it (there is a menu for this), and then after installing it locally, export it. Make sure to click in "export private key"