Golang App-engine OAuth Authorization

I am implementing an app-engine webapp written in Go that needs user authentication and authorization to access some user data on Google's APIs.

Do I still need to use the goauth2 and gorilla packages to implement authorization or is there some functionality in the "appengine" and "appengine/user" packages that implements Oauthorization natively for app-engine apps? I do not mind going ahead with goauth2, but if there is a better way...

You can use the "appengine/user" package for authentication with OAuth but I'm a fraid that you must implement authorization yourself.
For OAuth authentication with "appengine/user" package, see https://developers.google.com/appengine/docs/go/oauth/#Go_OAuth_and_App_Engine

Here's an example from the OAuth for Go Overview on the Google App Engine Docs site:

import (
    "fmt"
    "net/http"

    "appengine"
    "appengine/user"
)

func welcome(w http.ResponseWriter, r *http.Request) {
    c := appengine.NewContext(r)
    u, err := user.CurrentOAuth(c, "")
    if err != nil {
        http.Error(w, "OAuth Authorization header required", http.StatusUnauthorized)
        return
    }
    if !u.Admin {
        http.Error(w, "Admin login only", http.StatusUnauthorized)
        return
    }
    fmt.Fprintf(w, `Welcome, admin user %s!`, u)
}

It looks like appengine/user has the function user.CurrentOAuth() to provide authentication functionality.

For authorization, there's an example using OpenID Here.

There is a caveat; The documentation states:

> Note that using OAuth to identify your users is completely orthogonal to the standard user authentication modes. For example, pages marked with login: required or login: admin will refuse to load if the user is only authenticated via OAuth.

Full Go GAE reference available Here.