I have been trying to get a free SSL certificate to try out the MTLS feature of salesforce. Since I am still checking the feasibility of the feature, I felt it wouldn't be a good idea to buy a new certificate by paying the CA(trusted CAs on their list). I know I would be able to generate a certificate using LetsEncrypt by providing a public server URL link which I could use for my testing purposes as LetsEncrypt is in their trusted CA list. However, I do not have any public facing URL that I could use to generate the certs.
How shall I get the certificates in this case?