The resource owner password credentials grant lets the client use the resource owner's user name and password to get an access token directly. Although this grant might seem to conflict with an original OAuth goal of not having to share resource owner credentials with the client, it can makes sense in a secure context where other authorization grant types are not available, such as a client that is part of a device operating system using the resource owner credentials once and thereafter using refresh tokens to continue accessing resources. The following sequence diagram shows the successful process.
