We will locate the cert by its thumbprint.

On prem servers : you have installed the cert in on the server machine(s) that need to use it.

On Azure: You upload cert + must create app setting as explained here https://azure.microsoft.com/sv-se/blog/using-certificates-in-azure-websites-applications/

Pick the RestOperator you want to use with a client certificate - like RestPost in this send in user 'thumbprint' (case insensitive) and the thumprint of your installed cert in the password field.