server

var CompleteUserAuth = func(ctx iris.Context) (goth.User, error) {
	providerName, err := GetProviderName(ctx)
	if err != nil {
		return goth.User{}, err
	}

	provider, err := goth.GetProvider(providerName)
	if err != nil {
		return goth.User{}, err
	}
	session := sessionsManager.Start(ctx)
	value := session.GetString(providerName)
	if value == "" {
		return goth.User{}, errors.New("session value for " + providerName + " not found")
	}

	sess, err := provider.UnmarshalSession(value)
	if err != nil {
		return goth.User{}, err
	}

	user, err := provider.FetchUser(sess)
	if err == nil {

		return user, err
	}

	_, err = sess.Authorize(provider, ctx.Request().URL.Query())
	if err != nil {
		return goth.User{}, err
	}

	session.Set(providerName, sess.Marshal())
	return provider.FetchUser(sess)
}

var GetProviderName = func(ctx iris.Context) (string, error) {

	if p := ctx.URLParam("provider"); p != "" {
		return p, nil
	}

	if p := ctx.Params().Get("provider"); p != "" {
		return p, nil
	}

	if p := ctx.Values().GetString("provider"); p != "" {
		return p, nil
	}

	return "", errors.New("you must select a provider")
}

var SetState = func(ctx iris.Context) string {
	state := ctx.URLParam("state")
	if len(state) > 0 {
		return state
	}

	return "state"

}