Configure Amplify Cognito in Android and iOS to switch programmatically between USERNAME_PASSWORD and CUSTOM_AUTHENTICATION

You can not only set the Amplify configuration initially but also adjust per use.

So you can call Amplify.configure passing a patch to the settings sometimes.

Below you see an example where I used USER_SRP_AUTH and used a fallback to USER_PASSWORD_AUTH. (This is because when migrating users using Cognito Migration Triggers passwords need to be cleartext to be rehashed). But you can switch to custom auth.

The code is from a React project:

import Amplify from '@aws-amplify/core';
import Auth from '@aws-amplify/auth';

...

    handleSubmitLogin = async values => {
        const {
            login: { email, password }
        } = values;
        const { location: { search } } = this.props;
        try {
            let failed = false;
            try {
                Amplify.configure({
                    Auth: {
                    authenticationFlowType: 'USER_SRP_AUTH'
                    }
                });
                await Auth.signIn(email.trim().toLowerCase(), password);
            } catch(error) {
                console.log(error);
                failed = true;
            }
            if (failed) {
                Amplify.configure({
                    Auth: {
                        authenticationFlowType: 'USER_PASSWORD_AUTH'
                    }
                });
                await Auth.signIn(email.trim().toLowerCase(), password);   
            }      
            const params = queryString.parse((search || '?').substr(1));
            await this.props.handleLogin(params.ReturnUrl || '/profile/');
        } catch (e) {
            this.setState({ loginError: e.message });
        }
    };