Implement configurable auth providers

New providers need to "register" their URL scheme of choice in
auth.NewFromURL().

Implements: https://todo.sr.ht/~sircmpwn/tokidoki/1

cmd/tokidoki/main.go

@@ -16,9 +16,12 @@ import (
 
 func main() {
 	var (
-		addr string
+		addr    string
+		authURL string
 	)
 	flag.StringVar(&addr, "addr", ":8080", "listening address")
+	// TODO: make flag mandatory instead of default value
+	flag.StringVar(&authURL, "auth.url", "imaps://imap.migadu.com:993", "auth backend URL")
 	flag.Parse()
 
 	if len(flag.Args()) != 0 {
@@ -29,8 +32,10 @@ func main() {
 	mux := chi.NewRouter()
 	mux.Use(middleware.Logger)
 
-	// TODO: Configurable
-	authProvider := auth.NewIMAP("imap.migadu.com:993", true)
+	authProvider, err := auth.NewFromURL(authURL)
+	if err != nil {
+		log.Fatalf("failed to load auth provider: %s", err.Error())
+	}
 	mux.Use(authProvider.Middleware())
 
 	backend := storage.NewPostgreSQL()
@@ -41,7 +46,7 @@ func main() {
 		Handler: mux,
 	}
 	log.Printf("Server running on %s", addr)
-	err := server.ListenAndServe()
+	err = server.ListenAndServe()
 	if err != http.ErrServerClosed {
 		log.Fatalf("ListenAndServe: %s", err.Error())
 	}