CircleCI Server v3.x Authentication
CircleCI server currently supports OAuth through GitHub or GitHub Enterprise.
The default method for user account authentication in CircleCI Server is through GitHub.com/GitHub Enterprise OAuth.
After your installation is up and running, provide users with a link to access the CircleCI application - for example,
<your-circleci-hostname>.com – and they will be prompted to set up an account by running through the GitHub/GitHub
Enterprise OAuth flow before being redirected to the CircleCI login screen.