The user has already authorized my app to access Strava details. When the user logs in a second time, or from another device, they are prompted to enter their strava credentials as expected.
Once the do this, I expect them to be redirected back to my app, however, they are asked to re-authorize on Strava each time.
I did some testing and it looks like this might be related to the requested scopes. Can you try adding the read and profile:read_all scope and see if that fixes it?