Gitea login improve support

[soulteary]

After testing, it has been able to log in and authorize normally.

eg: https://github.com/soulteary/docker-sso-server/tree/main/example/howto-use-gitea

However, there are some improvements.

• [x] Automatic redirection after the first login
• [ ] Consider providing dedicated routing to make configuration easier.
• [ ] Gitea supports the definition of icons and needs to provide a good-looking icon, which allows users to customize in the future.