Passing parameters between the login and the callback functions

I'm in a weird situation where when I call the auth_callback, I need to know how the auth flow was initiated:

func Login(c *gin.Context) {
	var loginUrl LoginUrl
	if err := c.BindQuery(&loginUrl); err != nil {
		c.AbortWithStatus(http.StatusInternalServerError)
		return
	}

	var w http.ResponseWriter = c.Writer
	var req *http.Request = c.Request

	logger.Debug("Starting auth flow")
	url, err := gothic.GetAuthURL(c.Writer, c.Request)

	if err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
	}

	err = gothic.StoreInSession("is_web", strconv.FormatBool(loginUrl.IsWeb), req, w)
	c.Redirect(http.StatusFound, url)
}

func AuthCallback(c *gin.Context) {
	user, err := gothic.CompleteUserAuth(c.Writer, c.Request)
	fmt.Println("user: ", user)
	is_web, _ := gothic.GetFromSession("is_web", c.Request)
	fmt.Println("it's web or not", is_web)
}

Basically when I start the flow, I call mysite.com/auth/provider_name?is_web=true. I'm parsing the is_web parameter in the Login function, and I'm then trying to store it in the gothic session.

Then when AuthCallback is triggered, I'm trying to get is_web back, but the call to gothic.CompleteUserAuth raises an error: you must select a provider. I believe at this point the content of the session is overwritten? Does the call to StoreInSession wipe out the relevant info?

Start with the Login and AuthCallback entry points and trace gothic.GetAuthURL, StoreInSession, CompleteUserAuth, and GetFromSession through the shown request sequence. Reproduce the provider callback error and inspect how session state is preserved between requests. Done means determining whether storing is_web affects provider selection and documenting or correcting the resulting behavior.