LTI 1.3 requires working openssl functions to generate a private
key used for the JWT. Some installs (e.g. windows) can have the
functions available - but require configuration in php before they
actually do anything.
If the site is installed, and then the wwwroot changed, the plugin
config value for platformid for mod_lti is then stale, resulting in
OIDC errors. Given this config value was set using the wwwroot, we
should just be able to use the value of $CFG->wwwroot direcly, thus
avoiding this problem.