A principal database is described in which each entry includes one principal identity, and one or more alias identities that may each have an authorization scope. Principal identity attributes include a principal identifier and login credentials, and alias identity attributes include an authorization scope and login credentials. Responsive to successfully authenticating the user for a first application (a multiple-identity application), based on the alias identity login credentials, an access token containing both the alias identity attributes and the principal identity attributes is transmitted to the first application, causing the first application to grant a scope of access based on the authorization scope. Responsive to a request to authenticate the user for a second application (a single-identity application), the access token is transmitted to the second application without re-authenticating the user, causing the second application to grant a scope of access based on the principal identifier.