Jenkins & GitHub Enterprise Servers API endpoint error - requires POST

Question

TL;DR: This is a bug. There is a bug report. https://issues.jenkins-ci.org/browse/JENKINS-54051

I am trying to set up the API endpoint for Jenkins to know how to communicate with a GitHub Enterprise Server.

I am working behind a corporate proxy (though the error persists whether or not I have the proxy turned on) and my enterprise github has a custom CA cert that I think I've installed, but in either case I don't think that's the issue since I can't even connect it to the normal github api either. Here the is the error I am getting:

This error is for any endpoint, including https://github.myenterprise.com/api/v3 and https://api.github.com/ and even https://google.com. I can access these 3 sites through firefox without errors, and the github ones display the JSON stuff that I think I should get:

{
  "current_user_url": "https://api.github.com/user",
  "current_user_authorizations_html_url": "https://github.com/settings/connections/applications{/client_id}",
  "authorizations_url": "https://api.github.com/authorizations",
  ...
}

If I google "This URL requires POST" there are only 3 results, none of which relate to Jenkins. I have very limited API / HTML / REST experience and have no idea what to try to fix this.

Answer 1

It does look like this is a bug or mismatch between the latest versions of the github-branch-source plugin (v2.3.6) and the github plugin (v1.29.1). From a quick triage it looks like the affected call is https://github.com/jenkinsci/github-branch-source-plugin/blame/5646416554d58fe224be382baa021df1b601f302/src/main/java/org/jenkinsci/plugins/github_branch_source/Endpoint.java#L154 and the related changeset at https://github.com/jenkinsci/github-branch-source-plugin/commit/22d3383002274bc3f4368534eba2b5c852e78b39. This should be raised with the maintainers of the plugins concerned, unfortunately I'm off on holiday and don't have time to do this, but just posting my findings here to help the community in the meantime.

I don't advise this, but a workaround is to downgrade to the previous versions of the plugins: git 3.9.0, github 1.29.0 and github-branch-source 2.3.4 (only a good idea if your network is airgapped). Those plugin versions contains the serverside request forgery bugs so beware.