Setup private repo in Rancher Chart repository

gistfile1.yaml

Rancher only supports specific SSH key formats. When you try to add a ssh-key it often will fail and give the following error because the format is incorrect: 
data does not contain a valid RSA or ECDSA private key
This issue gave the idea that the Rancher interface has limited SSH key support: https://github.com/rancher/fleet/issues/138

Generate the private key and public key:
ssh-keygen -t rsa -b 4096 -m pem -C "Rancher chart ssh-key"

Since there is no password option in the Rancher interface, provide the keys without a passphrase and place the keys to a location of your choice. 
Test the key against Github to validate it is correct:
ssh-agent bash -c 'ssh-add /Users/USERNAME/.ssh/id_rsa_rancher_chart; git clone git@github.com:REPOSITORY/charts.git'

After you place these keys to the location of choice you can read them out and configure the pub key as a deploy key in Github. After this is done you can copy and paste the public and private key into Rancher ssh-key secrets while creating the repository. 
Use the SSH (not the https) url to configure the repository. The url should look like this:
git@github.com:REPOSITORY/charts.git