Yahoo OAuth 2.0 login malfunction

Today when I tried to access to my org SSO website using Yahoo OAuth 2.0, it failed and have the below behavior.

1. Initiate Yahoo OAuth flow, so it is now inside https://login.yahoo.com/config/login
2. Login page is shown, type in login name
3. Type in password
4. After loading for a while... It will go back to Login page in Step 2
5. Repeat Step 2-3

It was definitely working before without the above bug, anybody else is experiencing the same bug and/or know how to fix this?

Edit on 10 May 2019,

The Yahoo OAuth 2 login flow is down again, maybe wait a few months and it will work again...

Tested on 31 Aug 2018,

The Yahoo OAuth 2 login flow is working again, probably Yahoo team fixing their bug.