Passing data to non wordpress application

The only way to pass data to an external url without writing custom PHP is using the confirmation redirect. This is under Form Settings and then the Confirmation tab. You can then build a custom query string and name the fields whatever you want when building your custom query string. You then use the form field variables to pass the value of that field using the form field variable drop down.

However, the login form for the application you are using would have to be requesting this data from the query string. So it's not going to automatically populate these fields without writing some custom code to interact with the 3rd party application.

Any reason you are trying to use a Gravity Forms form to redirect to another login form where they would still have to click login in order to login? Seems like an extra step that is unnecessary and puts them more clicks away from actually logging in.

No, the field names cannot be changed. They are generated dynamically by Gravity Forms.

However, if you know what you are doing you can use available API hooks to take this information and when the form is submitted repurpose it and submit it again to whatever form handler you need to handle the login. This is possible, although becomes problematic if the user enters the wrong login and this makes validation difficult.