Hello Brian, sorry for the delayed response.
You are using 4.2.2 in Ubuntu 20.04.
About the `SAMLRequest` parameter, it's encoded using base64 and urlencode, even that I may be wrong.
**Have it worked before with other IDP?**
Also would you please provide:
1. `oxauth.log` (please set it in `TRACE` level)
3. `passport.log` (please set it in `DEBUG` level)
4. A screnshot of your configured passport provider.