logs: use %o to format error

otherwise, they are printed as multi-line and this messes up tail+date formatting

src/oidc.js

@@ -131,7 +131,7 @@ function load(modelName) {
     try {
         data = JSON.parse(fs.readFileSync(filePath), 'utf8');
     } catch (e) {
-        debug(`load: failed to read ${filePath}, start with new one.`, e);
+        debug(`load: failed to read ${filePath}, start with new one. %o`, e);
     }
 
     DATA_STORE[modelName] = data;
@@ -618,7 +618,7 @@ async function renderError(ctx, out, error) {
         errorMessage: error.error_description || error.error_detail || 'Unknown error'
     };
 
-    debug('renderError:', error);
+    debug('renderError: %o', error);
 
     ctx.type = 'html';
     ctx.body = ejs.render(fs.readFileSync(path.join(__dirname, 'oidc_templates/error.ejs'), 'utf8'), data, {});