For Apache and IIS it is described on pages 3-4 of the IOPLEX Jespa Operators Manual and is mentioned in our install instructions. The page from Atlassian - Integrating JIRA with NGINX, can serve as a reference for general configuration of NGINX when used with Atlassian products.
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Once you reconfigured your NGINX this way the telltale sign of it working will be in jespa.log at log level 4 - see *bold values*, showing the remote client's IP address and port as opposed to proxy's one. Some values have been obscured with ****