How to configure Salesforce in OnPremise
Add in stackend/.env the following environment variables:
# stackend/.env
SALESFORCE_CLIENT_ID={your-salesforce-consumer-key}
SALESFORCE_CLIENT_SECRET={your-salesforce-consumer-secret}
App Flow Enablement and Security

App Settings

You can find your secrets on Apps > External Client Apps > Your App > OAuth Settings

To create your app you can follow the official guide: https://help.salesforce.com/s/articleView?id=xcloud.connected_app_client_credentials_setup.htm&type=5
Check how OAuth 2.0 Web Server Flow work for Web App Integrations: https://help.salesforce.com/s/articleView?id=platform.ev_relay_create_connected_app.htm&type=5