How are users accessing the service? (describe user authentication methods)

Access to DESelect is provided through single sign-on (SSO) for Salesforce Marketing Cloud users. Users have to be logged into Salesforce Marketing Cloud to be able to use DESelect. The DESelect application is available under the AppExchange menu and opens as an iframe inside of Salesforce Marketing Cloud.

User access to the DESelect application is managed by Administrators within Salesforce Marketing Cloud.

Please also read How does DESelect authenticate Marketing Cloud users?