It would be nice to be able to match headers based on regular expressions. Some simple use cases could be matching based on Cookies, where a specific type of user is making a request.

Depending on the library being used (e.g., PCRE vs something else), for maintaining performance, it might be okay to explicitly ask the user to specify whether the header match block contains a regex or not, with a isregex:true entry. For example,

"headers" : [
                          {
                              "name" : "Cookie",
                              "value" : "user=test-.*?",
                              "isregex" : true
                          }
                      ]

In the absence of the isregex block, the header match can be considered as simple string equality checks.