Use GitHub as the IdP for the OAuth integration

[yhwang]

Current OAuth/OpenID integration supports several IdPs, including Okta, Google, IBM App ID, and more. However, when I tried to integrate with the GitHub OAuth flow, it failed. It would be good to support the GitHub OAuth flow.

Expected Behavior or Use Case

For GitHub OAuth, it would go with the OAuth flow:

• Get access token from https://github.com/login/oauth/access_token
• Use the access token to get user info from https://api.github.com/user

Presto Component, Service, or Connector

presto-main, OAuth2

Possible Implementation

Enhance the OAuth flow to support GitHub access tokens and user info endpoints.

[yhwang]

Based on the GitHub doc here, we need:

• Accept: application/json header to get the JSON payload from the access token endpoint.
• GitHub also requires the User-Agent header as well.
• GitHub OAuth doesn't enforce expiration. We need to make the exp claim optional.

[yhwang]

While investigating the GitHub OAuth flow integration, I found our /logout path for the OAuth flow doesn't work properly. Let me also fix that while working on the GH OAuth integration.