YahooImpl doesn't work

[bogdan-nourescu]

Hello,
I am writing to let you know that the YahooImpl doesn't work anymore with OAuth1.
I have changed the code to work with OAuth2, but you need to consider this changes:

ENDPOINTS.put(Constants.OAUTH_AUTHORIZATION_URL,
                "https://api.login.yahoo.com/oauth2/request_auth");
ENDPOINTS.put(Constants.OAUTH_ACCESS_TOKEN_URL,
                "https://api.login.yahoo.com/oauth2/get_token");

Use OAuth2. In OAuth2 you also need to change the method from GET to POST for OAUTH_ACCESS_TOKEN_URL (line 114)

I will make a pull request for it, but i am just posting in case there is someone searching for why Yahoo is not working anymore.

[bogdan-nourescu]

Added the pull request for the upgrade from OAuth 1 to OAuth2
#107