I'm currently trying the same thing, but for a login suing IIAMS so in other words with authentication ids and tokenids generated by HTTP POST commands.
It seems in theory very doable, but ... I'm currently blocked due to a limit of 1000 chars for using variables in pre/post execution scripts. As the generated authID is almost 2000 chars, I can't post the entire request body, so authentication fails.
Unless... someone knows how to maybe change this limit to +2000 chars???