In response to Oz Linden's comment
I know that this is a specialized way and doesn't address most cases, but it fits my needs.
I use OAuth2 in my scripts.
When a script starts, it presents client credentials to an authentication server.
It receives an access token back, which the script remembers (below). This oath2header is added to all the HTTP requests from the script.
list oauth2header = [HTTP_CUSTOM_HEADER,"Authorization","Bearer " + llJsonGetValue(body, ["access_token"])];
The benefit I receive is middleware on my server rejects all requests that don't