feat: Add email config test on provider edit page (#819)

* feat: Add email config test on provider edit page

* Re-use send-email API

* Optimize code

Optimize code

* Update service.go

* Update service.go

Co-authored-by: Gucheng <85475922+nomeguy@users.noreply.github.com>

web/src/TestEmailWidget.js

@@ -0,0 +1,59 @@
+// Copyright 2021 The Casdoor Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import * as Setting from "./Setting";
+
+export function sendTestEmail(provider, email) {
+  testEmailProvider(provider, email)
+    .then((res) => {
+      if (res.msg === "") {
+        Setting.showMessage("success", `Successfully send email`);
+      } else {
+        Setting.showMessage("error", res.msg);
+      }
+    })
+    .catch(error => {
+      Setting.showMessage("error", `Failed to connect to server: ${error}`);
+    });
+}
+
+export function connectSmtpServer(provider) {
+  testEmailProvider(provider)
+    .then((res) => {
+      if (res.msg === "") {
+        Setting.showMessage("success", `Successfully connecting smtp server`);
+      } else {
+        Setting.showMessage("error", res.msg);
+      }
+    })
+    .catch(error => {
+      Setting.showMessage("error", `Failed to connect to server: ${error}`);
+    });
+}
+
+function testEmailProvider(provider, email = "") {
+  let emailForm = {
+    title: provider.title,
+    content: provider.content,
+    sender: provider.displayName,
+    receivers: email === "" ? ["TestSmtpServer"] : [email],
+    provider: provider.name,
+  }
+
+  return fetch(`${Setting.ServerUrl}/api/send-email`, {
+    method: "POST",
+    credentials: "include",
+    body: JSON.stringify(emailForm)
+  }).then(res => res.json());
+}