It looks like the disappearance of the Get Token link is a bug (NIM093798); it shouldn't be hidden. Thank you for bringing this to our attention. 🙂
http://<server ip>:6080/arcgis/tokens?request=getToken&username=<username>&password=<password>&expiration=5
http://<server ip>:6080/arcgis
For AGS 10.2.2, the documentation is available at:
http://<server>:6080/arcgis/sdk/rest/index.html#/Generate_Token/02ss00000059000000/