It's not possible to use alphanumerical login in recommendation client, but it should be.

Steps to reproduce:
1. Set up recommendation:
config/packages/ezrecommendation.yaml

ezrecommendation:
  system:
    default:
      export:
        authentication:
          method: basic
          login: user
          password: password
      authentication:
(...)

2. Login as admin into your application
3. Go to Content -> Content Structure
4. Click "Create" button

Expected:
Content creation form is opened

Actual:
Exception:

Return value of EzSystems\EzRecommendationClient\Value\Config\ExportCredentials::getLogin() must be of the type int, string returned