Fix OAuth authentication by passing instance_url to AuthManager

[jessems]

OAuth Authentication Fix Summary

Problem: OAuth authentication was failing because AuthManager._get_oauth_token() was trying to access oauth_config.instance_url, but the OAuthConfig class only has a token_url field, not an instance_url field.

Solution: Pass the instance URL separately to the AuthManager constructor from the main server configuration.

Required Changes:

1. src/servicenow_mcp/auth/auth_manager.py:

   • Add instance_url: str = None parameter to __init__()
   • Store as self.instance_url = instance_url
   • In _get_oauth_token(), replace oauth_config.instance_url with self.instance_url
   • Add proper error handling if instance_url is None

2. src/servicenow_mcp/server.py:

   • Update AuthManager instantiation from:

     self.auth_manager = AuthManager(self.config.auth)

   • To:

     self.auth_manager = AuthManager(self.config.auth, self.config.instance_url)

3. Enhanced OAuth flow (optional but recommended):

   • Implement both client_credentials and password grant types
   • Use proper Basic Auth headers for OAuth token requests
   • Add detailed logging for debugging OAuth issues

This allows the AuthManager to access the instance URL needed for constructing the OAuth token endpoint URL when token_url is not explicitly configured.

[anandsainath]

LGTM, fix it then ship it.

[anandsainath]

Can you remove these?