Ah... sounds like that should be relaxed perhaps.... can you create a JIRA for this please?
A workaround for you might be to override the HttpMessageComposer class.
I tried...Jira requires me to login (again), and it gives me a login error. I have the same problem when trying to sign a cla.
I reported this 3-4 weeks ago, there were a few replies none of them resolved the problem. Nothing in the site logs.