Render a template upon failed POST request [golang]

I want to handle the errors of a POST request and re-render the form with the errors displayed above it, but the only solution to handling errors I see is http.Error() but this returns a plaintext response, not an HTML page. Is there a way to executeTemplate() and re-render the html page with the form? Am I supposed to redirect the user to the same page? If so, how do I pass the error information to that redirected page?

Edit: So, when I use this code, and try to executeTemplate, the Post request returns a 200 status code (which is wrong) and it re-renders blank page, not the template I specified.

func PostSignup(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
if r.Method != http.MethodPost {
	http.Error(w, http.StatusText(405), http.StatusMethodNotAllowed)
	return
}

usr := users.User{}
usr.Username = r.FormValue("username")
usr.Email = r.FormValue("email")
usr.Hash = r.FormValue("password")

errors := CredErrors{}
errors.Error = "Username cannot be blank"
if usr.Username == "" {
	// http.Error(w, "Username cannot be blank.", 400)
	tpl.ExecuteTemplate(w, "signup.gothml", errors)
	return
}

The answer is in the question:

> Is there a way to executeTemplate() and re-render the html page with the form?

Yes, use executeTemplate to re-render the form. http.Error() is for returning HTTP errors, not form validation errors. If the form fails validation and you want to redisplay it, do just that - render the form out to the browser again, with whatever validation errors/prepopulation/whatever you want to display.