If you setup a simple backend endpoint / workflow per the below with a Login (or Signup) action within it then you’ll get a unique access key for that user within the response.
You’ll need to call this endpoint using the API Connector (rather than Schedule API Workflow) in order to get the response back with the token and expiry date inside.
Endpoint to issue token
Response when you call that endpoint from the API Connector
You can find more on it here under Authentication