UHTTP does not support client verification when using https, this limits our ability to support a bunch of restful web services,.
It is currently not possible to change the content of the HTTP header created by the SOAP U2.0 connector; when using (e.g.) cURL you can override or add information to the header

The asn setting $macro_first can be used to determine the order that macro instructions are processed – before or after all other input. If it were available as proc code, the order could be determined as the individual components require.