Thank you very much, that would have taken me forever to figure out. This works great!
$user->{section} = $self->{c}->stash->{lti_jwt_claims}{'https://purl.imsglobal.org/spec/lti/claim/custom'}{canvas_section_id};
$user->{section} = $self->{c}->stash->{lti_jwt_claims}{'https://purl.imsglobal.org/spec/lti/claim/custom'}{canvas_section_id};