Ah, I just tested this out and if you don't need it in the JWT, you should be able to see it in the registrations object returned after login.
Here's a response I get after logging in:
{ "token": "ey...", "user": { "active": true, "connectorId": "e3306678-a53a-4964-9040-1c96f36dda72", "email": "email@example.com", "id": "2df13f18-01cc-48a4-b97a-2ab04f98d006", "insertInstant": 1592857899119, "lastLoginInstant": 1596819645662, "lastUpdateInstant": 0, "passwordChangeRequired": false, "passwordLastUpdateInstant": 1592857899145, "registrations": [ { "applicationId": "78bd26e9-51de-4af8-baf4-914ea5825355", "id": "73d2317b-d196-4315-aba2-3c205ed3ccae", "insertInstant": 1592857899151, "lastLoginInstant": 1592857899153, "lastUpdateInstant": 1596813810104, "roles": [ "Role1" ], "usernameStatus": "ACTIVE", "verified": true } ], "tenantId": "1de156c2-2daa-a285-0c59-b52f9106d4e4", "twoFactorDelivery": "None", "twoFactorEnabled": false, "usernameStatus": "ACTIVE", "verified": true } }So user.applicationId.roles is what you want. Note that roles are applied on an application by application basis. If a user is in a group which has a role 'roleA' which is created in 'applicationA', but is not registered for 'applicationA', they won't receive that role. More on that here: https://fusionauth.io/docs/v1/tech/core-concepts/groups