feat: add three idp support by goth. (#351)

1. add 3 providers: apple, azuread(v1) and slack.
2. support importing providers from goth.

Signed-off-by: 0x2a <stevesough@gmail.com>

web/src/auth/AppleLoginButton.js

@@ -0,0 +1,32 @@
+// Copyright 2021 The casbin 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 {createButton} from "react-social-login-buttons";
+import {StaticBaseUrl} from "../Setting";
+
+function Icon({ width = 24, height = 24, color }) {
+    return <img src={`${StaticBaseUrl}/buttons/apple.svg`} alt="Sign in with Apple" style={{width: 24, height: 24}} />;
+}
+
+const config = {
+    text: "Sign in with Apple",
+    icon: Icon,
+    iconFormat: name => `fa fa-${name}`,
+    style: {background: "#ffffff", color: "#000000"},
+    activeStyle: {background: "#ededee"},
+};
+
+const AppleLoginButton = createButton(config);
+
+export default AppleLoginButton;