Use Request Headers

All http headers specified in project properties are by default included with each request item and will be part of each request that will be generated from the request item. You can, however, change this behavior for particular request item in the 'Headers' tab of request item properties. The following options are available:

Additionally include the following headers with every request

If you want some headers to be included with particular request item only and you do not want to define them as project headers, enter them in this field. Each header must be specified on a separate line, name and value for each header must be separated by a colon.
Headers specified in this field will override project headers with the same name.

Parameters and chaining

It is possible to use parameters or chaining items in the field for additional headers; you can press 'Ctrl+Space' or 'Ctrl+Shift+Space' to see the list of available data.