Even though the JIRA plugin for Jenkins is able to handle JIRA sessions, it does not reuse them, causing two major issues:

(1) Performance
The performance of the "build page" is very poor because for every build, the plugin needs to poll JIRA hundreds of times and creates hundreds of new session. While API requests are usually pretty fast (especially via the new REST API), their performance drops drastically if every requests needs to create a new session.

(2) Load on JIRA
Since the plugin creates hundreds of new sessions, it puts a lot more load than necessary on the issue tracker. It also makes administration user sessions in JIRA useless because they cannot be found between the flood of jenkins jira plugin sessions.

Root cause:
All of the methods create a new session for every single call: