Starting 15.2.0 GoCD Server will expose authentication end-point. What this means is GoCD users can add “custom” authentication schemes through plugins.
Examples of integrations possible:
- OAuth Login - GitHub, Google, Hotmail, Yahoo! etc.
 - Single Sign-on (SSO) - LDAP, Okta etc.
 - 2-factor authentication - SMS verification etc.
 - Custom 
username&passwordauthentication 
How does it work?
Below is an explanation of how GitHub OAuth Login plugin works.
- Generate OAuth token on GitHub.
 
  - On plugin listing page users will see a gear icon (similar to one on the pipeline dashboard).
 
  - Clicking on the gear icon opens a pop-up that renders “Plugin Settings”.
 
  - Login Page
 
  - Click on GitHub icon
 
  - Successful login
 
  - Ability to Search & Add users
 
  We hope plugin developers are able to use this feature to support their organizations authentication mechanism.
References:
As always, GoCD questions can be asked on the mailing list.