User Level: 

By default, Drupal gives us the ability to apply several roles to a user.

In OSU Drupal, however, this can be problematic and confusing, as we use the Groups module to apply access control to most content contributors and this provides a whole other set of permissions that need to be maintained. It's much more direct, and less bug prone, for us to have progressive permissions versus the combinatorial ones that can be created by combining multiple roles on a user.

To limit users to a single role, we need to make use of a contributed module called Single User Role.

Set-up is simple - basically it gets installed and just works right out of the gate. Following is an example of how this module affects the ability to assign roles.

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D8 - Working With People - Roles - Single User Role - Default Roles

1. Default User Roles

When we look at user roles on a user's account screen, we can see all roles listed, each with a checkbox.

D8 - Working With People - Roles - Single User Role - All Roles Assigned

2. Multiple Role Assignments

This allows for the application of all roles to a single user, which can be problematic in terms of permission collisions.

D8 - Working With People - Roles - Single User Role - Roles in User List

3. Roles in User List

Additionally in can clutter up the User List and and make it confusing for users

D8 - Working With People - Roles - Single User Role - Checkboxes Gone

4. Checkboxes Gone

Once the Single User Role module has been added, the checkboxes that are used for role designation on a user's account form are removed and replaced with a select field.

D8 - Working With People - Roles - Single User Role - Select Box Only Allows One Choice

5. Only One Selection Allowed

The select field that's provided only allows for a single selection.