Updates or modifies an existing role membership.
If a role A is granted to a role B, then role A is said to have role B as a member. These relationships are described in the “members” portion of the returned JSON.
When the members query parameter is provided, you will get the members of a role.
When the members and member query parameters are provided, the role specfified by
member will be added as a member of the role specified in the endpoint URI.