HI Chandra,
you have to select “Require Client Certificates”, if you are looking only certification based authentication
Request Client Certificates
Integration Server requests client certificates for all requests. If the client does not provide a certificate, the server prompts the client for a userid and password
Require Client Certificates
Integration Server requires client certificates for all requests.
refer HTTPS configuration in IS administator guide
let me know if you have any concern.
#Integration-Server-and-ESB#webMethods