Revert "remove obsolete sendError() function"

This reverts commit 5d9b122dd5.

src/routes/oauth2.js

@@ -171,6 +171,17 @@ function sendErrorPageOrRedirect(req, res, message) {
     }
 }
 
+function sendError(req, res, message) {
+    assert.strictEqual(typeof req, 'object');
+    assert.strictEqual(typeof res, 'object');
+    assert.strictEqual(typeof message, 'string');
+
+    res.render('error', {
+        adminOrigin: config.adminOrigin(),
+        message: message
+    });
+}
+
 // Main login form username and password
 function loginForm(req, res) {
     if (typeof req.session.returnTo !== 'string') return sendErrorPageOrRedirect(req, res, 'Invalid login request. No returnTo provided.');
@@ -192,12 +203,12 @@ function loginForm(req, res) {
     }
 
     settings.getCloudronName(function (error, name) {
-        if (error) return sendErrorPageOrRedirect(req, res, 'Internal Error');
+        if (error) return sendError(req, res, 'Internal Error');
 
         cloudronName = name;
 
         clientdb.get(u.query.client_id, function (error, result) {
-            if (error) return sendErrorPageOrRedirect(req, res, 'Unknown OAuth client');
+            if (error) return sendError(req, res, 'Unknown OAuth client');
 
             // Handle our different types of oauth clients
             var appId = result.appId;