You can define app roles and configure directory extension optional claims as described here.
B2C doesn't directly support RBAC. The way to pass specific claims in Token issued by B2C is by configuring it in User Flows or Custom Policies at this time. You would use custom attributes passed as claims.
There is also a set of admin roles available. https://azure.microsoft.com/en-us/updates/b2c-admin-roles-preview/