Merge pull request #1584 from testfirstcoder/improve-youngest-key-search

improve youngest key search

src/IdentityServer/Services/Default/KeyManagement/KeyManager.cs

@@ -242,7 +242,7 @@ internal bool IsKeyRotationRequired(IEnumerable<KeyContainer> allKeys)
             {
                 // there are younger keys, then they might also be within the window of the key activation delay
                 // so find the youngest one and treat that one as if it's the active key.
-                activeKey = keys.OrderByDescending(x => x.Created).First();
+                activeKey = keys.MaxBy(x => x.Created);
             }
 
             // if no younger keys, then check if we're nearing the expiration of active key
@@ -624,7 +624,7 @@ internal KeyContainer GetCurrentSigningKeyInternal(IEnumerable<KeyContainer> key
         // discovery). we don't want the second server using a key that's not in the first server's
         // discovery document. this will be somewhat mitigated by the initial duration where we 
         // deliberately ignore the cache.
-        var result = keys.OrderBy(x => x.Created).First();
+        var result = keys.MinBy(x => x.Created);
         return result;
     }