Get OAuth2 user information

curl --request GET \
  --url https://api.fluxer.app/v1/oauth2/userinfo \
  --header 'Authorization: Bearer <token>'

{
  "sub": "<string>",
  "id": "<string>",
  "username": "<string>",
  "discriminator": "<string>",
  "global_name": "<string>",
  "avatar": "<string>",
  "email": "<string>",
  "verified": true,
  "flags": 1073741823
}