How to login to Cognito from a client app?

Hi - Thanks for checking. You can check Integrating Amazon Cognito authentication and authorization with web and mobile apps reference page which covers working with Amplify and SDKs. AWS Amplify is a complete solution for building web and mobile applications. With Amplify, you can connect to existing resources with the Amplify libraries, or you can create and configure new resources with the Amplify command line interface (CLI). Amplify also has connected UI components like Authenticator for setup and customization of the sign-in and sign-up experience in your app.