feat: add casdoor as saml idp support (#571)

* feat: add casdoor as saml idp support

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

* fix: merge code

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

* fix: modify response value

Signed-off-by: Steve0x2a <stevesough@gmail.com>

* fix: modify samlResponse generation method

Signed-off-by: Steve0x2a <stevesough@gmail.com>

* fix: generating a response using etree

Signed-off-by: Steve0x2a <stevesough@gmail.com>

* fix: change metadata url

Signed-off-by: Steve0x2a <stevesough@gmail.com>

* fix: modify front-end adaptation

Signed-off-by: Steve0x2a <stevesough@gmail.com>

* fix: recovering an incorrect override

Signed-off-by: Steve0x2a <stevesough@gmail.com>

* fix: change the samlResponse location

Signed-off-by: Steve0x2a <stevesough@gmail.com>

* fix: add relayState support

Signed-off-by: Steve0x2a <stevesough@gmail.com>

controllers/saml.go

@@ -0,0 +1,33 @@
+// Copyright 2022 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.
+
+package controllers
+
+import (
+	"fmt"
+
+	"github.com/casdoor/casdoor/object"
+)
+
+func (c *ApiController) GetSamlMeta() {
+	host := c.Ctx.Request.Host
+	paramApp := c.Input().Get("application")
+	application := object.GetApplication(paramApp)
+	if application == nil {
+		c.ResponseError(fmt.Sprintf("err: application %s not found", paramApp))
+	}
+	metadata, _ := object.GetSamlMeta(application, host)
+	c.Data["xml"] = metadata
+	c.ServeXML()
+}