The username and private key credential used to authenticate with the ACS clusters master node. This is the private key paired with the SSH RSA public key provided when you create the ACS cluster (see Deploy a Docker container hosting solution using the Azure portal ).

The username and key credentials can be updated from Azure Portal. Find the Virtual Machine for your ACS cluster master node from the portal, and you can update the credential from SUPPORT + TROUBLESHOOTING >>> Reset password page.