Version 2 (Json)
Access is gained using Basic authentication See wikipedia
Download the swagger file from:
https://<server>/<application>/rest/v2/swagger.json
You can browse and try the api, using the built in SwaggerUI (from version 9147):
https://<server>/<application>/rest/v2/swagger
GET examples:
Single:
https://<server>/<application>/rest/v2/<entity>/<DataID>
List:
https://<server>/<application>/rest/v2/<entity>