I know a few people have asked about how to integrate CAPM's OpenAPI with Tableau for reporting. There are a few things needed in order to make this work but the first thing is to make sure there are no firewalls blocking access. If that's all clear you can try this out and you should get a list of columns to select for building reports.
NOTE: One critical item is that you have to make sure the query return format is set to atom
From the CAPM 2.8 documentation:
This sample query can be leveraged:
(you'll need your CAPC user credentials and you'll use the PC for the query. The default port is 8181)