Authorization code flow with custom UI and Cognito

Hi,

It is not currently possible to implement oauth2 authorization code flow without using hosted UI for authentication, this is because there is no public API to retrieve the authorization code itself from Cognito and it has to be passed back to hosted UI after successful authentication.

If you want to use custom UI, you can either just use the SDK to authenticate users using InitiateAuth API or Amplify SignIn (this is not oauth2), or if you must use oauth2 then you need to build your oauth2 endpoints on top of Cognito APIs (similar to Amplify identity broker).