3-Legged OAuth, with Services 7.x-3.3, REST Server using PHP
In Drupal with Services 3 modules, if you go to admin/structure/services/list/[endpoint name]/authentication you have choices under Default
You are browsing documentation for an older version of Drupal, which is not supported any longer, and the information may not be correct. See current documentation for Contributed modules
OAuth 3.x Guide, Documentation and FAQ go here. OAuth Module is a part of the Services module.
In Drupal with Services 3 modules, if you go to admin/structure/services/list/[endpoint name]/authentication you have choices under Default