BTW, by default the LTI setup will only create accounts with permission level TA or lower. If someone is a professor in the LMS and does not already have a professor account in the WeBWorK course, then they should get an error when they click on the LTI link.
In that case, I would say leave all of the other settings in the Authen_LTI.conf file, with the exception of the secret. Then you can simply add the secret to the course.conf file.