[USER SUBMITTED GUIDE] How to access the new MAL API using OAuth 2.0

GET https://api.myanimelist.net/v2/users/@me?fields=id,name,anime_statistics

Authorization: Bearer a1b2c3d4

{
    "id": 5292566,
    "name": "ZeroCrystal",
    [...],
    "anime_statistics": {
        "num_items_watching": 8,
        "num_items_completed": 718,
        [...],
        "mean_score": 6.48
    }
}

def generate_code_verifier
  verifier = SecureRandom.urlsafe_base64(64).gsub(/[^A-Za-z0-9\-._~]/, '')
  verifier[0...128] # Ensure the verifier length is between 43 and 128 characters
end
def generate_code_challenge(verifier)
  base64_url_encoded_sha256 = Base64.urlsafe_encode64(Digest::SHA256.digest(verifier)).gsub(/[^A-Za-z0-9\-._~]/, '')
  base64_url_encoded_sha256[0...128] # Ensure the challenge length is between 43 and 128 charactersend
end

http://localhost/oauth 

{"error":"invalid_request","message":"The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed.","hint":"Authorization code has expired"}