[Golang] Realize client user login based on OAuth2.0 WeChat scanning code (principle + code implementation + video explanation)

Foreword:

Careful summary, including principle + configuration + detailed implementation of code

Principle explanation

What is OAuth2.0

OAuth 2.0 is an authorization protocol used to authorize third-party applications to access user resources without providing the user's credentials (such as username and password) directly to the third-party application. This authorization mechanism provides users with better security while allowing users to