...
2- Where can we create those roles?
A role is a personality that a user assumes to perform a specific set of operations.
A role includes a set of rights and privileges.
A user assumes that role inherits those rights and privileges.
https://docs.openstack.org/admin-guide/cli-manage-projects-users-and-roles.html
Authorization Model in OpenStack (keystone API V2.0)
https://prosuncsedu.wordpress.com/2014/02/13/authorization-model-in-openstack/
root@super4:~# openstack role list
+----------------------------------+-----------------+
| ID | Name |
+----------------------------------+-----------------+
| 03be779481894d9196cb94ec77c17234 | admin |
| 0d7d26cab3914c01b3696d0fcf3426e3 | ResellerAdmin |
| 47f70b9bacd74ce6885c9dd9efa3b9da | heat_stack_user |
| 9fe2ff9ee4384b1894a90878d3e92bab | _member_ |
+----------------------------------+-----------------+
...