suricata-update net.py section usefully allows setting arbitrary HTTP headers. This is a minimal extraction and adaptation of lines allowing execution.

net.py

import re

def is_header_clean(header):
    if len(header) != 2:
        return False
    name, val = header[0].strip(), header[1].strip()
    if re.match( r"^[\w-]+$", name) and re.match(r"^[\w\s -~]+$", val):
        return True
    return False


url = ("https://example.com/feed", "Authorization: Basic YXR6QGNvcmVsaWdodC5jb206bXlwYXNzd29yZA==")
if isinstance(url, tuple):
    header = url[1].split(":") if url[1] is not None else None
    if header and is_header_clean(header=header):
        name, val = header[0].strip(), header[1].strip()
        print("Setting HTTP header %s to %s" % (name, val))
    elif header:
        print("Header not set as it does not meet the criteria")
    url = url[0]