Enhance Backdoor retrieval and update credentials

Updated `TryGet` method in `BackdoorExtensions.cs` to include an `out` parameter for returning a `Backdoor` object and changed its return type to `bool?`. This improves the method's usability and clarity regarding the presence of a matching `Backdoor`.

Modified `backdoors.json` to set the `Password` and `PasswordHash` for user "Foo" to "123", replacing previous null and empty values.

src/DigitalData.Auth.API/Models/BackdoorExtensions.cs

@@ -4,5 +4,12 @@ public static class BackdoorExtensions
 {
     public static Backdoor? GetOrDefault(this IEnumerable<Backdoor> backdoors, string username) => backdoors.Where(b => b.Username == username).FirstOrDefault();
 
-    public static Backdoor? TryGet(this IEnumerable<Backdoor> backdoors, string username) => backdoors.Where(b => b.Username == username).FirstOrDefault();
+    public static bool? TryGet(this IEnumerable<Backdoor> backdoors, string username, out Backdoor backdoor)
+    {
+        var _backdoor = backdoors.Where(b => b.Username == username).FirstOrDefault() ?? default;
+#pragma warning disable CS8601
+        backdoor = _backdoor;
+#pragma warning restore CS8601
+        return _backdoor is not null;
+    }
 }

src/DigitalData.Auth.API/backdoors.json

@@ -2,8 +2,8 @@
   "backdoors": [
     {
       "Username": "Foo",
-      "Password": null,
-      "PasswordHash": ""
+      "Password": "123",
+      "PasswordHash": "123"
     }
   ]
 }