Setup a dedicated identity provider for kaiyuanshe.cn

[adieu]

Currently the authentication flow is very simple:

+--------+
| Github |
+---+----+
    |
    v
+---+----+
|  Web   |
+---+----+
    |
    v
+---+----+
| Server |
+--------+

To make the whole system more pluggable and welcoming developers from different background, I suggest to setup a dedicated identity provider just like linux foundation did at https://identity.linuxfoundation.org/

The target architecture could be something like this:

+---------+   +--------+   +--------+
| Google  |   | Github |   | Email  |
+----+----+   +---+----+   +----+---+
     |            |             |
     |            |             |
+----v------------v-------------v---+
|           Identity Provider       |
+----+------------+-------------+---+
     |            |             |
     |            |             |
+----v----+   +---v----+   +----v---+
|  Web    |   | Server |   | Store  |
+---------+   +--------+   +--------+

I have experience setting up an identity provider using dex ( https://github.com/dexidp/dex ) with great success. There are other open source idp systems out there. As long as they all support openid connect, we could use any of them.