Error response enhancements, CoreID auth client backend

src/util/cache/Cache.ts

@@ -1,4 +1,5 @@
 import {Awaitable} from '../support/types'
+import {Safe} from '../support/Safe'
 
 /**
  * Abstract interface class for a cached object.
@@ -11,6 +12,14 @@ export abstract class Cache {
      */
     public abstract fetch(key: string): Awaitable<string|undefined>;
 
+    /**
+     * Fetch a value from the cache by its key as a Safe value.
+     * @param key
+     */
+    public async safe(key: string): Promise<Safe> {
+        return new Safe(await this.fetch(key))
+    }
+
     /**
      * Store the given value in the cache by key.
      * @param {string} key