integrate only oauth2 in rails app without doorkeeper

I have been check and tested how doorkeeper works. I am new to oauth/oauth2, so I am puzzled if it can work alone without doorkeeper or grape. The question is can I create authentication using oauth/oauth2 alone? How can I possible do it. For example, I have a store app and I want to integrate oauth2 for my API, how can I possibly do it? Can anybody give me an idea or give some bunch of links of tutorials?

Thanks!