Extract Variable Pattern to Header with Multi value

[dpatty]

Hi All , 

I have to extract one header value inside API proxy . 

Example: 

Header name = cert_app 

Header Value1   cn=api.google.com,org=google,type=search,reg=us

Header Value2  org=google,cn=api.google.com,type=search,reg=us

Header Value3  org=google,type=search,reg=us,cn=api.google.com,

I have to extract cn=api.google.com from the header value to a variable . Basically this can come at start ,end or in between of the string which is separated by comma.

Appreciate suggestion on this.

Best Regards,

Patty