After enabling GitHub SSO, you might be unable to access CircleCI pages (settings, projects, etc...).
When you enable SSO old OAuth tokens are not safelisted for use, so you will need to re-create them after enabling SSO with the following steps:
- Log into the affected organization on GitHub using SSO.
- Go to OAuth application settings > https://github.com/settings/applications.
- Select the CircleCI token and revoke it.
- Go to circleci.com and log out if necessary.
- Log back in -which should prompt you to grant authorization- and make sure CircleCI is authorized to access the organization.