traefik plugin 0.7.7 (#73)

* Automatic discovery of the scopes.

Issue #61 raised very valid concerns about users configuring scopes that are not supported by the provider.
This change introduces automatic discovery of supported scopes by fetching the provider's discovery document and filtering out unsupported scopes.

Before:
User configures: scopes: ["openid", "profile", "email", "offline_access"]
Self-hosted GitLab: "The requested scope is invalid, unknown, or malformed"
Authentication: ❌ FAILS

After:
User configures: scopes: ["openid", "profile", "email", "offline_access"]
Middleware checks discovery doc → offline_access not supported
Automatically filters to: ["openid", "profile", "email"]
Authentication: ✅ SUCCEEDS

* Resolves issue #74 by enabling user to specify expected audience in the configuration.

* Fix flaky tests.

logger_singleton.go

@@ -11,12 +11,30 @@ var (
 	singletonNoOpLogger *Logger
 	// noOpLoggerOnce ensures the singleton is created only once
 	noOpLoggerOnce sync.Once
+	// noOpLoggerMu protects access to the singleton logger during reset
+	noOpLoggerMu sync.RWMutex
 )
 
 // GetSingletonNoOpLogger returns the singleton no-op logger instance.
 // This reduces memory allocation by reusing the same no-op logger
 // instance across the entire application.
 func GetSingletonNoOpLogger() *Logger {
+	noOpLoggerMu.RLock()
+	if singletonNoOpLogger != nil {
+		logger := singletonNoOpLogger
+		noOpLoggerMu.RUnlock()
+		return logger
+	}
+	noOpLoggerMu.RUnlock()
+
+	noOpLoggerMu.Lock()
+	defer noOpLoggerMu.Unlock()
+
+	// Double-check after acquiring write lock
+	if singletonNoOpLogger != nil {
+		return singletonNoOpLogger
+	}
+
 	noOpLoggerOnce.Do(func() {
 		singletonNoOpLogger = &Logger{
 			logError: log.New(io.Discard, "", 0),
@@ -29,6 +47,9 @@ func GetSingletonNoOpLogger() *Logger {
 
 // ResetSingletonNoOpLogger resets the singleton instance (mainly for testing)
 func ResetSingletonNoOpLogger() {
+	noOpLoggerMu.Lock()
+	defer noOpLoggerMu.Unlock()
+
 	noOpLoggerOnce = sync.Once{}
 	singletonNoOpLogger = nil
 }