func BeginAuthHandler(res http.ResponseWriter, req *http.Request) {
	url, err := GetAuthURL(res, req)
	if err != nil {
		res.WriteHeader(http.StatusBadRequest)
		fmt.Fprintln(res, err)
		return
	}
	http.Redirect(res, req, url, http.StatusTemporaryRedirect)
}
/*
BeginAuthHandler is a convienence handler for starting the authentication process.
It expects to be able to get the name of the provider from the query parameters
as either "provider" or ":provider".

BeginAuthHandler will redirect the user to the appropriate authentication end-point
for the requested provider.

See https://github.com/markbates/goth/examples/main.go to see this in action.
package gothic
import (
	"errors"
	"fmt"
	"net/http"
	"os"
	"github.com/gorilla/sessions"
	"github.com/markbates/goth"
)
const SessionName = "_gothic_session"
var Store sessions.Store
var defaultStore sessions.Store
var keySet = false
func init() {
	key := []byte(os.Getenv("SESSION_SECRET"))
	keySet = len(key) != 0
	Store = sessions.NewCookieStore([]byte(key))
	defaultStore = Store
}