rest - Android 앱에서 Salesforce에 사례를 만들고 싶습니다

사례를 작성하기 위해 Salesforce에 REST API가 있습니다. Android/IOS 앱에서 동일한 API에 액세스하여 사례를 작성하려고합니다. 여기서 내 문제는 인증입니다.

1. We are using OAuth 2.0 user agent flow for authentication because in username-password we need to expose username and password so we don't want to use that flow to get the access token. In User Agent flow should the user need to enter the password or it will authorize based on authorization code?

2. If user need to enter the password how we will avoid because the user will be customer they don't have any password and username ,can we store password and use it to for logging automatically.

미리 감사합니다