Authenticate Jenkins CI for Github private repository

Perhaps GitHub's support for deploy keys is what you're looking for? To quote that page:

When should I use a deploy key?

Simple, when you have a server that needs pull access to a single private repo. This key is attached directly to the repository instead of to a personal user account.

If that's what you're already trying and it doesn't work, you might want to update your question with more details of the URLs being used, the names and location of the key files, etc.

Now for the technical part: How to use your SSH key with Jenkins?

If you have, say, a jenkins unix user, you can store your deploy key in ~/.ssh/id_rsa. When Jenkins tries to clone the repo via ssh, it will try to use that key.

In some setups, you cannot run Jenkins as an own user account, and possibly also cannot use the default ssh key location ~/.ssh/id_rsa. In such cases, you can create a key in a different location, e.g. ~/.ssh/deploy_key, and configure ssh to use that with an entry in ~/.ssh/config:

Host github-deploy-myproject    HostName       github.com    User           git    IdentityFile   ~/.ssh/deploy_key    IdentitiesOnly yes

Because all you authenticate to all Github repositories using git@github.com and you don't want the above key to be used for all your connections to Github, we created a host alias github-deploy-myproject. Your clone URL now becomes

git clone github-deploy-myproject:myuser/myproject

and that is also what you put as repository URL into Jenkins.

(Note that you must not put ssh:// in front in order for this to work.)

One thing that got this working for me is to make sure that github.com is in ~jenkins/.ssh/known_hosts.

If you need Jenkins to access more then 1 project you will need to:
1. add public key to one github user account
2. add this user as Owner (to access all projects) or as a Collaborator in every project.

Many public keys for one system user will not work because GitHub will find first matched deploy key and will send back error like "ERROR: Permission to user/repo2 denied to user/repo1"

http://help.github.com/ssh-issues/