Extend GitHub OAuth to Support GitHub Enterprise

[devangtomar]

1. Is your feature request related to a problem? Please describe.

   Currently, the GithubOAuthProvider in the Chainlit repository only supports the standard GitHub URL for authorization and token retrieval. This limitation prevents users from utilizing custom GitHub instances, which require a different base URL for OAuth operations.

2. Describe the solution you'd like

   I propose extending the GithubOAuthProvider class to support custom GitHub URLs by allowing the URL to be specified as an environment variable, similar to how OAUTH_GITHUB_CLIENT_ID and OAUTH_GITHUB_CLIENT_SECRET are handled. This change would involve modifying the oauth_providers.py file to include a new environment variables, OAUTH_GITHUB_CUSTOM_URL and OAUTH_GITHUB_CUSTOM_API_URL, and updating the authorization and token URLs accordingly.

   Here is the code that needs to be changed in oauth_providers.py:

   class GithubOAuthProvider(OAuthProvider):
       id = "github"
       env = ["OAUTH_GITHUB_CLIENT_ID", "OAUTH_GITHUB_CLIENT_SECRET", "OAUTH_GITHUB_URL"]
       authorize_url = os.environ.get("OAUTH_GITHUB_URL", "https://github.com") + "/login/oauth/authorize"
   
       def __init__(self):
           self.client_id = os.environ.get("OAUTH_GITHUB_CLIENT_ID")
           self.client_secret = os.environ.get("OAUTH_GITHUB_CLIENT_SECRET")
           self.authorize_params = {
               "scope": "user:email",
           }
   
           if prompt := self.get_prompt():
               self.authorize_params["prompt"] = prompt
   
       async def get_token(self, code: str, url: str):
           base_url = os.environ.get("OAUTH_GITHUB_URL", "https://github.com")
           payload = {
               "client_id": self.client_id,
               "client_secret": self.client_secret,
               "code": code,
           }
           async with httpx.AsyncClient() as client:
               response = await client.post(
                   f"{base_url}/login/oauth/access_token",
                   data=payload,
               )
               response.raise_for_status()
               content = urllib.parse.parse_qs(response.text)
               token = content.get("access_token", [""])[0]
               if not token:
                   raise HTTPException(
                       status_code=400, detail="Failed to get the access token"
                   )
               return token
   
       async def get_user_info(self, token: str):
           base_url = os.environ.get("OAUTH_GITHUB_URL", "https://api.github.com")
           async with httpx.AsyncClient() as client:
               user_response = await client.get(
                   f"{base_url}/user",
                   headers={"Authorization": f"token {token}"},
               )
               user_response.raise_for_status()
               github_user = user_response.json()
   
               emails_response = await client.get(
                   f"{base_url}/user/emails",
                   headers={"Authorization": f"token {token}"},
               )
               emails_response.raise_for_status()
               emails = emails_response.json()
   
               github_user.update({"emails": emails})
               user = User(
                   identifier=github_user["login"],
                   metadata={"image": github_user["avatar_url"], "provider": "github"},
               )
               return (github_user, user)```

Describe alternatives you've considered

An alternative could be to manually modify the URLs in the code for each custom GitHub instance, but this approach is not scalable or user-friendly.

Additional context

By implementing this change, users will be able to configure the OAuth provider to work with their GitHub instances by setting the OAUTH_GITHUB_CUSTOM_URL and OAUTH_GITHUB_CUSTOM_API_URL environment variables.