Jira returns HTTP/503 instead of HTTP/403 or HTTP/404 when a JS source map is requested

Issue Summary

This is reproducible on Data Center: yes

Steps to Reproduce

1. Open any Jira page.
2. Open the browser's developer tools.
3. Click on Sources, and then open any JavaScript resource (example shown below).

Expected Results

Jira responds with HTTP/403 Forbidden or HTTP/404 Not found since source maps are not available. The RFC 2616 Hypertext Transfer Protocol – HTTP/1.1 states the following:

10.4 Client Error 4xx

The 4xx class of status code is intended for cases in which the
client seems to have erred.

Therefore, it's the client who committed a mistake by requesting a non-existing resource.

Actual Results

Jira responds with HTTP/503 Service Unavailable, which, according to RFC 2616

10.5 Server Error 5xx

Response status codes beginning with the digit "5" indicate cases in
which the server is aware that it has erred or is incapable of
performing the request.

This class of errors is intended for temporary situations that a retry might fix. Most software is designed to retry after a while when encountering these errors, which makes no sense since Jira won't provide a source map.

Workaround

None.