How to provide OAuth based API when application itself relies on thrid part OAuth

I have a Java web application. It relies on Google开发者_JS百科 OAuth to authenticate and authorize users. I want to provide an API to my application which must also use OAuth. Is it possible to provide OAuth by myself without having a database of users and auth mechanism? Has it been implemented by anyone?

The OAuth specification doesn't make any particular statements about how to authenticate (ie, login) users - just how to pass credentials to other servers, once the authentication succeeds. There's no particular reason that, at the step where other servers might put up a login box, you can't instead initiate an OAuth transaction with another unrelated server.

However, you will need to have some sort of database to link up the credentials you issue (ie, the credentials your clients will use to operate your API) with the credentials you receive from upstream servers - whether this data needs to be retained over server shutdowns, etc, will depend on whether you want your third-party clients to be able to use their credentials over a long period.