return meaningful error for disabled users (#13968)

fixes #13958

cmd/signature-v4-utils.go

@@ -154,6 +154,11 @@ func checkKeyValid(r *http.Request, accessKey string) (auth.Credentials, bool, A
 		// Check if the access key is part of users credentials.
 		ucred, ok := globalIAMSys.GetUser(r.Context(), accessKey)
 		if !ok {
+			// Credentials will be invalid but and disabled
+			// return a different error in such a scenario.
+			if ucred.Status == auth.AccountOff {
+				return cred, false, ErrAccessKeyDisabled
+			}
 			return cred, false, ErrInvalidAccessKeyID
 		}
 		cred = ucred