RLS - Rest API to get roles for generating embed token

[Anonymous]

Rest EndPoint: https://api.powerbi.com/v1.0/myorg/groups/<groupID>/reports/<reportID>/GenerateToken

body: {
         "accessLevel": "View",
        "identities": [{"username": "<email>", "roles": [ "roleA"], "datasets": ["9377d1f1-6a25-4206-2c53befd40be"] }]
        }
In this "RoleA" is manually given, My question is "How do we get the roles of a user for a particular dataset using REST API for generating embed token?"

 

 Any help is really appreciated