feature: basic auth0 support (#78)

* feature: basic auth0 support

* refactor: improve auth flow

* refactor: extract HttpServer config

* feature: merge HTTP API layer with Let's Encrypt

management/http_server/handler/logout.go

@@ -0,0 +1,48 @@
+package handler
+
+import (
+	"net/http"
+	"net/url"
+)
+
+// Logout logs out a user
+type Logout struct {
+	authDomain   string
+	authClientId string
+}
+
+func NewLogout(authDomain string, authClientId string) *Logout {
+	return &Logout{authDomain: authDomain, authClientId: authClientId}
+}
+
+// ServeHTTP redirects user to teh auth identity provider logout URL
+func (h *Logout) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+
+	logoutUrl, err := url.Parse("https://" + h.authDomain)
+
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	logoutUrl.Path += "/v2/logout"
+	parameters := url.Values{}
+
+	var scheme string
+	if r.TLS == nil {
+		scheme = "http"
+	} else {
+		scheme = "https"
+	}
+
+	returnTo, err := url.Parse(scheme + "://" + r.Host + "/login")
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	parameters.Add("returnTo", returnTo.String())
+	parameters.Add("client_id", h.authClientId)
+	logoutUrl.RawQuery = parameters.Encode()
+
+	http.Redirect(w, r, logoutUrl.String(), http.StatusTemporaryRedirect)
+}