I propose making a single authentication plug-in for both your Discourse app and Atlassian Jira. From the two forum threads listed, I see that you have been toying with this idea for several years. Thus, I think you can bear with my 60-day delivery timeframe. If awarded, I would spend my first week reviewing the documentation for OAuth2, Discourse, and Atlassian Jira. Thereafter, I anticipate almost-daily communication and pull requests.
By the way, it appears that you are based in Australia. Although I have never stepped foot in your fair country, I must mention that I am a fan of the NRL's Gold Coast Titans, and AFL's Sydney Swans and North Melbourne Kangaroos.
All told, I think you would very satisfied with my level of diligence.
Sincerely,
Benjamin Tuohy