I decided to play around with creating templates in XML and being able to push them via the RESTful API in ISE.
The first thing I need to do is to enable the REST API in ISE. In order to do so, navigate to Administration>System>Settings and choose the radio button for Enable ERS for Read/Write
The next thing that you would need to do is create an ERS admin that is part of the ERS Admin group. Navigate to Administration>System>Admin Access>Admin Users and click Add>Create Admin User. Create the following user:
After this is configured, you should be able to test the ERS API by opening POSTMAN. In my case, I used a Chrome POSTMAN plug-in.
ISE supports basic authentication so you want to plug your ERS Admin credentials in:
Click on Refresh Headers and then add an Accept header with the following value: application/vnd.com.cisco.ise.identity.internaluser.1.0+xml;charset=UTF-8
Now test out the ERS API by sending a GET request to https://<ise-url>/ers/config/internaluser/versioninfo
Congratulations! You've now got the ERS API working!