Matches requests where a request header with a specified name (argument1) matches the given header-value (argument2). The match must be exact, rather than a substring of the header value. The match is case sensitive.

<match:request-header operation="name-value-cmp" argument1="User-Agent" argument2="Custom Agent">

!name-value-cmp matches if either the given header name is not present or its value doesn't match the one specified in metadata.