Use the cognito-idp create-user-pool-client sub-command to create a user pool client, as follows:

aws cognito-idp create-user-pool-client 
    --user-pool-id us-east-1_fYsb1Gyec 
    --client-name my-user-pool-client 
    --explicit-auth-flows ADMIN_NO_SRP_AUTH 
    --profile admin

Here, I have specified ADMIN_NO_SRP_AUTH as an explicit auth flow. This will allow us to pass our username and password without SRP. Other options that are allowed include CUSTOM_AUTH_FLOW_ONLY and USER_PASSWORD_AUTH. A few other authentication flows, including USER_SRP_AUTH and REFRESH_TOKEN_AUTH, are supported by default. We will see REFRESH_TOKEN_AUTH within this recipe, and USER_SRP_AUTH within a different recipe.