https://console.developers.google.com/project

https://developers.google.com/drive/web/about-auth
https://developers.google.com/accounts/docs/OAuth2
https://developers.google.com/+/features/sign-in

+curl sample:
https://developers.google.com/accounts/docs/OAuth2WebServer

OAuth libs:
https://github.com/scribejava/scribejava/wiki/getting-started
https://habrahabr.ru/company/hh/blog/278957/

ratpack-oauth:
https://github.com/uris77/ratpack-oauth-example

request:
...?
    client_id=...
    &redirect_uri=...
    &response_type=code

response:
    302 Location: "<redirect_uri>?code=...."
    Now the client app should quickly (~10s) exchange the auth-code to access-token

access-token request:
POST <...>/get_token
    Authorization: "Basic" + base64encode(<client_id> + ":" + <client_secret>)
    Content-Type: application/x-www-form-urlencoded
    Body:
        redirect_uri=....
        &grant_type=authorization_code
        &code=...

response:
{
    "access_token": "Jz.....cuaos-",
    "token_type": "bearer,
    "expires_in": 3600,
    "refresh_token": "AOi...RFlA-",
    "xoauth_yahoo_guid": "JT...OCE"
}

now we can use the obtained access_token:

GET https://social.yahooapis.com/v1/me/guid
    ?format=json
    &access_token=Jz...cuaos-

response:
{
    "guid" : {
        "value": "P2AY...JW7P",
        "uri": "https://social.yahooapis.com/v1/me/guid"
    }
}

And, finally, we can use the obtained value with the access_token for further actions:

GET https://social.yahooapis.com/v1/user/P2AY...JW7p/profile
    ?format=json
    &access_token=Jz...cuaos-
    
response:
{
    // user profile info goes here
}