Unable to install or update Add-ons via UPM due to Invalid anti-XSRF token provided
Universal Plugin Manager is unable to install new add-ons or update existing add-ons.
The following error message is displayed: "Invalid anti-XSRF token provided. The valid token should be retrieved transparently, but you may want to perform a hard refresh in your browser and try again before creating a support issue"
JIRA is being accessed through a proxy server.
The proxy server appears to be introduce this error, but exact cause of this issue is currently unknown.
Install plugin manually by file upload: Installing add-ons by file upload
Bypass the proxy server and access JIRA directly to install plugins via the UPM.