I need to setup my rest endpoint to authenticate using Digital Certificates. When doing research about mutual authentication the examples are only using soap. https://help.salesforce.com/articleView?id=security_keys_uploading_mutual_auth_cert_api.htm&type=5

Do I have to login and get the session ID using soap and then I can use the session ID to access the REST endpoint? Or is there a way to login via REST? This is assuming that the client making the calls digital certificate is saved in the salesforce org.