Error:
400 Bad Request: "The `redirect_uri` parameter must be a Login redirect URI in the client app settings:..."
Solution:
Make sure that the redirect uri is pointing at the backend uri and not the frontend. We do authorization through our backend. Therefore, if Okta is not redirecting to the Cortex backend, you'll see the above error. An easy way to find whether or not this is set up correctly is to take a look at the URL in your address bar that you've been redirected to. If you copy and paste the address up to the end of login/oauth2/code/okta into your redirect_uri in Okta, you should then be able to log in.