In-Memory example doesn't work

westlakem

I'm using the in-memory model and the code from the first page and I'm getting a lot of "model does not implement" errors. For example: ``` "Invalid argument: model does not implement `saveAuthorizationCode()`" ```

vijayantkatyal

same issue. have to create / import some functions manually for this to work. you can use docs to fix this. https://oauth2-server.readthedocs.io/en/latest/model/spec.html#saveauthorizationcode-code-client-user-callback