Third party app login integration

We are trying to connect a login page on the website we’ve created and have it connect directly to an app dashboard that is hosted on Tableau so that when the user inputs their name and password on the Webflow site it then take directly into the third-party app’s dashboard.

This appears to require custom code so my question is how complex is this process and what are the prices to be expected if one was to hire someone to complete this process?

Thank you!

Here is my site Read-Only: