Jenkins Poll SCM Plugin vulnerable to Cross-Site Request Forgery

Poll SCM Plugin was not requiring requests to its API be sent via POST, thereby opening itself to Cross-Site Request Forgery attacks. This allowed attackers to initiate polling of projects with a known name. While Jenkins in general does not consider polling to be a protection-worthy action as it's similar to cache invalidation, the plugin specifically adds a permission to be able to use this functionality, and this issue undermines that permission.