You can login using a java-action
For example
ISession session = Core.login(username, password);
See apidocs
Be aware that Mendix sets cookies for session information.
Hi , See these forum posts for more reference
https://forum.mendix.com/questions/5487/Login%20form#8512
https://forum.mendix.com/questions/5488/How%20do%20I%20make%20a%20login%20form%20with%20a%20login%20button?#8511