Thanks Leon, I did some further checking and then interacting with Cengage further revealed we were using the wrong URL which was intended for LTI that is supported only by Moodle version 3.10+. Now that we've provided the supposed right URL the 400 response stopped and we got to second base. And now we have a new problem which Cengage is stumped by. Something to do with "Invalid Issuer". So I think their public key may be unable to be verified based on the verbiage of the message.
This endeavor has prompted me to push for an update of our Moodle from 3.8.x to 3.10.x. I've been asking for permission to upgrade to 3.9.x for over a year (smile) but while I'm the administrator, I'm not the one making the choices of the school. We have school administrators that were busy working on other projects for the past year to approve the new design changes that stem from core theme changes (Boost, namely).
Hopefully when we get Moodle 3.10.x installed, we will be able to use the self-registration function for Cengage that they wanted us to use primarily.
This endeavor has prompted me to push for an update of our Moodle from 3.8.x to 3.10.x. I've been asking for permission to upgrade to 3.9.x for over a year (smile) but while I'm the administrator, I'm not the one making the choices of the school. We have school administrators that were busy working on other projects for the past year to approve the new design changes that stem from core theme changes (Boost, namely).
Hopefully when we get Moodle 3.10.x installed, we will be able to use the self-registration function for Cengage that they wanted us to use primarily.