You can use the operatorCompanyId header in the REST API to impersonate a user as tenant operator. When a REST API call is issued, the role associated with the tenant operator for the company takes effect and enables the tenant operator to perform the operation.
Example
This REST API creates a disk library as a tenant operator for the company with ID 10.
POST <webservice>/Library HTTP/1.1
Host: client.mydomain.com
Accept: application/xml
Authtoken: QSDK 38568012f4d1e8ee1841d283a47aa3ba78e124ea58354b5fc6
0f4dab8a63347d05cf5552484dafda3bfa4c5db84e580b1cb37bcf8e65b39f7f
8549a443e6f78a2c7be3f31b3d845e24776c835e498e8e883bb40c46bd15af4f
40ca94e823acedcdd4e9659e74b34a07a85c4586cd2ed914b6dce015874783ef7
68fda78183a4208930954a377f66eb56c8b92cexampl4s437a19317ca6ce7f323
3d5a01aca35dbad93468b833f2cf71010809006a937670adce711ca8be46638e8
Content-type: application/xml
operatorCompanyId: 10
<EVGui_ConfigureStorageLibraryReq isConfigRequired="1">
<library mediaAgentId="1234" libraryName="library001" mountPath="c:\library001" loginName="" password="" opType="1"/>
</EVGui_ConfigureStorageLibraryReq>