add basic suppport for client_credentials oauth grant

Foxchat.Identity/Utils/OauthUtils.cs

@@ -0,0 +1,23 @@
+namespace Foxchat.Identity.Utils;
+
+public static class OauthUtils
+{
+    public static readonly string[] Scopes = ["identify", "chat_client"];
+
+    private static readonly string[] ForbiddenSchemes = ["javascript", "file", "data", "mailto", "tel"];
+    private const string OobUri = "urn:ietf:wg:oauth:2.0:oob";
+
+    public static bool ValidateRedirectUri(string uri)
+    {
+        if (uri == OobUri) return true;
+        try
+        {
+            var scheme = new Uri(uri).Scheme;
+            return !ForbiddenSchemes.Contains(scheme);
+        }
+        catch
+        {
+            return false;
+        }
+    }
+}