Hi Andy,
what exactly are you trying to achieve? I can interpret your request in multiple ways, e.g.
- Customer logs in. Credentials should be stored permanently in a cookie or other means so the user does not have to enter their credentials ever again <-- This can be done in the hybrid mobile app. I don't know of any webbrowser-based solution for this, and would also introduce a security risk..
- Customer enters the app as anonymous user and signs in using some third-party authentication (e.g. OAuth, login with facebook/google credentials). Or the user needs access to functionality that is only available when logged on <-- in this case, check out Ronald's suggestion or the Oauth module from the appstore.
- Customer enters the app as anonymous user, performs some actions, then needs to log on to confirm. For example filling a shopping cart as an anonymous user, then log on to receive a discount or get shipping address. By logging on the session data is lost, which means the shopping cart will be empty <-- In this case, it is possible to use the 'Sign in microflow' which can be configured in the "Anonymous user" tab in the project Security settings. This takes the anonymous user and the signed in user as parameters and can be used to transfer data between the anonymous sessions and the logged on session. See also https://docs.mendix.com/refguide6/project-security#anonymous-users for more information
Sorry if I misunderstood your question, feel free to correct and/or elaborate on the use case you need a solution for...