I am getting unknown_ca error for ssl handshake while hitting a REST web service through LISA. When I hit the webservice through browser, it says the certificate is not trusted but there is an option to ignore this and after which evreything works fine.
How can i replicate this behavior in LISA i.e to ignore untrusted certificates and get the response.
DevTest (formerly LISA) is a system test tool, and, as such, cannot be configured to ignore security errors.
The SSL/TLS implementation is the standard Java implementation - in Java the Certificate Authorities are stored in a file called "cacerts" that lives in the Java installation - adding the correct certificates to this file should resolve your issue.
DevTest ships with its own Java run-time, so the file you would need to update is located under your installation directory in jre/lib/security.
For more information on how Java and thus DevTest uses SSL, please see Of SSL, SNI, Java and DevTest