Over 59% of APIs use some other type of Auth other than OAuth2. And authentication is just one piece of the integration puzzle.
Authentication and authorization are fundamental to exposing data and services via APIs, providing simple authentication and identity based access control. This lets the API provider know which client is connecting and what features or data they have access to.
These companies have more than 1,031 internal cloud services, so getting every app to work together is a major necessity.
SOURCE: SMARTBEAR STATE OF APIS 2016