providers/radius: fix inverted message authenticator validation (#17855)

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

internal/outpost/radius/request.go

@@ -1,7 +1,6 @@
 package radius
 
 import (
-	"bytes"
 	"crypto/hmac"
 	"crypto/md5"
 	"errors"
@@ -46,7 +45,7 @@ func (r *RadiusRequest) validateMessageAuthenticator() error {
 		return err
 	}
 	hash.Write(encode)
-	if bytes.Equal(mauth, hash.Sum(nil)) {
+	if !hmac.Equal(mauth, hash.Sum(nil)) {
 		return ErrInvalidMessageAuthenticator
 	}
 	return nil