How to get role name in Power BI app owns data embedded API

use link https://docs.microsoft.com/en-us/power-bi/developer/embedded/embedded-row-level-security to do embedded, in RLS it ask to change code like:

var generateTokenRequestParameters = new GenerateTokenRequest("View", null, identities: new List<EffectiveIdentity> { new EffectiveIdentity(username: "username", roles: new List<string> { "roleA", "roleB" }, datasets: new List<string> { "datasetId" }) });

var tokenResponse = await client.Reports.GenerateTokenInGroupAsync("groupId", "reportId", generateTokenRequestParameters);

I try to find a way to get roles programmatically, but I can't find any API call can do that. Anyone