OAuth PKCE code_verifier and code_challenge generator implimented golang.
// Create code_verifier
v := CreateCodeVerifier()
code_verifier := v.String()
// Create code_challenge with plain method
code_challenge := v.CodeChallengeS256()
code_challenge_method := "plain"
// Create code_challenge with S256 method
code_challenge := v.CodeChallengeS256()
code_challenge_method := "S256"