Enabling the RPC plugin
To invoke JIRA operations remotely, you should ensure that the RPC plugin is enabled on the JIRA installation you are targeting. If you simply want to create a client to http://jira.atlassian.com/ then you can skip this step. First you need to check if the Accept Remote API Calls has been enabled in 'General Configuration' under 'Global Settings' in the left-hand menu:
Then you need to enable the JIRA RPC Plugin in 'Plugins' under 'System' in the left-hand menu:
To get the source code of the RPC plugin, see https://bitbucket.org/atlassian_tutorial/jira-rpc-plugin
Your server should now be ready to accept remote procedure calls.