Merge pull request #26834 from bdach/2fa-cancel-crash

Fix crash when logging out during 2FA email verification

osu.Game/Online/API/OAuth.cs

@@ -128,19 +128,12 @@ private bool ensureAccessToken()
             // if we already have a valid access token, let's use it.
             if (accessTokenValid) return true;
 
-            // we want to ensure only a single authentication update is happening at once.
-            lock (access_token_retrieval_lock)
-            {
-                // re-check if valid, in case another request completed and revalidated our access.
-                if (accessTokenValid) return true;
-
-                // if not, let's try using our refresh token to request a new access token.
-                if (!string.IsNullOrEmpty(Token.Value?.RefreshToken))
-                    // ReSharper disable once PossibleNullReferenceException
-                    AuthenticateWithRefresh(Token.Value.RefreshToken);
+            // if not, let's try using our refresh token to request a new access token.
+            if (!string.IsNullOrEmpty(Token.Value?.RefreshToken))
+                // ReSharper disable once PossibleNullReferenceException
+                AuthenticateWithRefresh(Token.Value.RefreshToken);
 
-                return accessTokenValid;
-            }
+            return accessTokenValid;
         }
 
         private bool accessTokenValid => Token.Value?.IsValid ?? false;
@@ -149,14 +142,18 @@ private bool ensureAccessToken()
 
         internal string RequestAccessToken()
         {
-            if (!ensureAccessToken()) return null;
+            lock (access_token_retrieval_lock)
+            {
+                if (!ensureAccessToken()) return null;
 
-            return Token.Value.AccessToken;
+                return Token.Value.AccessToken;
+            }
         }
 
         internal void Clear()
         {
-            Token.Value = null;
+            lock (access_token_retrieval_lock)
+                Token.Value = null;
         }
 
         private class AccessTokenRequestRefresh : AccessTokenRequest