How to store client credentials in Appian securely?

I need to generate a secure embedded link and need to put that in an Appian interface. I mimicked what given in this documentation here (https://help.sigmacomputing.com/docs/example-embed-api-and-url) and created an expression rule for the same. It works but there are some organization level restriction to not put up client id and client secret in constants. Could you please share any alternatives which can be used to store the credentials in Appian or any workaround for the same? I tried to look into Third Party Credentials store but it seems like it can be accessed via a plugin alone.