Got the latest LTS version of Jenkins with current jenkins-jira-plugin and a JIRA 6.4 installation.
I can log in to JIRA without issue and in the configuration I can see that the Remote API is indeed switched on.
When I do a wget from our Jenkins box against JIRA I get told I'm not authenticated - perfect.
When I configure the JIRA plugin within Jenkins using my credentials I hit "Validate" and get told Failed to authenticate.
Checked the Jenkins logs and I find a stack trace. An HTTP response has been received - HTML output with markup that I've failed to authenticate. The stack trace itself says it expected a JSON response!
I'm sure this must be pretty fundamental. Does it somehow require a more recent version of JIRA or something that I've not spotted?
Thanks,
James