OAuth 2.0
OLX API implements OAuth2 standard. For more information you can visit https://www.oauth.com/oauth2-servers/definitions/.
Basic principle of OAuth is one point of authorization and accessing all of resources with access token, granting (or not) access to certain endpoints.
OAuth access token is string which should be passed to every request made to OLX API endpoints. Token is valid for certain amount of time, after that application have to send request with refresh token to receive new token.
Remember Access token is like password - when someone obtains token, then gains full access to given account, limited only by token scope.
In order to use API partner should request to receive API Client data. One partner may have more than one application eligible for OLX API, each with different set of credentials. Basic API credentials are client_id and client_secret - both are required regardless of selected authentication method.