extracted interfaces for services, to aid in creating tests

src/Service/DomainInterface.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace App\Service;
+
+interface DomainInterface {
+    /** IE: "auth.example.com" or null if not using a separate subdomain
+     * @return ?string Returns auth subdomain if configured, otherwise null */
+    public function getAuthSubdomain(): ?string;
+
+    /** check if given url is an acceptable url for redirection
+     * @param string $url Where we are thinking of sending the user
+     * @return bool Returns true if it is acceptable to send the user there */
+    public function validReturn(string $url): bool;
+
+    /** check if host-base matches auth-base
+     * @param string $host
+     * @return bool returns true if and only if host matches base domain of auth */
+    public function matchesAuth(string $host): bool;
+
+    /** IE: "example.com" if central auth is something like "auth.example.com"
+     * @return string|null returns base domain if we are doing central auth */
+    public function authBase(): ?string;
+}