Fixing CodeQL Warnings (#6277)

# Description

Fixing code scanning warnings:
https://github.com/radius-project/radius/security/code-scanning.

## Type of change
- This pull request is a minor refactor, code cleanup, test improvement,
or other maintenance task and doesn't change the functionality of Radius
(issue link optional).

Fixes: #6081 

## Auto-generated summary

<!--
copilot:all
-->
### <samp>🤖 Generated by Copilot at 527e660</samp>

### Summary
🔒🛠️🧪

<!--
1. 🔒 - This emoji represents security, which is the main theme of these
changes. The `sanitizeUrl` function prevents open redirect
vulnerabilities, and the `html` package prevents XSS attacks.
2. 🛠️ - This emoji represents fixing or improving something, which is
what the changes do for the UCP API and the test package. The
`sanitizeUrl` function improves the validation of the URL path, and the
`html` package improves the escaping of the request body.
3. 🧪 - This emoji represents testing, which is the context of the
`httpbaseline` package. The changes affect how the test mock responses
are generated and handled.
-->
Improved the security of the UCP API and its tests by sanitizing URL
paths and escaping HTML in responses. Added a `sanitizeUrl` function in
`pkg/ucp/resources/url.go` and used the `html` package in
`test/ucp/httpbaseline/baseline.go`.

> _We sanitize the URL, we don't trust the path_
> _We escape the body, we avoid the wrath_
> _Of the evil hackers, who lurk in the dark_
> _They can't redirect us, they can't leave their mark_

### Walkthrough
* Sanitize URL path to prevent open redirect vulnerabilities in UCP API
([link](https://github.com/radius-project/radius/pull/6277/files?diff=unified&w=0#diff-205044f118b5c4ccc5d1c4c9ac53023e648e8d9888bb8a25aaf572a57640a132R31-R32),
[link](https://github.com/radius-project/radius/pull/6277/files?diff=unified&w=0#diff-205044f118b5c4ccc5d1c4c9ac53023e648e8d9888bb8a25aaf572a57640a132R66-R72))
* Escape request body to prevent XSS vulnerabilities in UCP API testing
([link](https://github.com/radius-project/radius/pull/6277/files?diff=unified&w=0#diff-8ca92e0087efe40d9d3317cd14b0e76816be54a550ad56d578bad1c5533a45ffR23),
[link](https://github.com/radius-project/radius/pull/6277/files?diff=unified&w=0#diff-8ca92e0087efe40d9d3317cd14b0e76816be54a550ad56d578bad1c5533a45ffL205-R207))

Co-authored-by: Yetkin Timocin <[email protected]>

pkg/ucp/resources/url_test.go

@@ -24,11 +24,11 @@ import (
 
 func Test_ExtractPlanesPrefixFromURLPath_Invalid(t *testing.T) {
 	data := []string{
-		"planes/radius", // Not long enough
-
-		"planes//foo", // Empty segment
-
+		"planes/radius",                      // Not long enough
+		"planes//foo",                        // Empty segment
 		"/subscriptions/test/anotherone/bar", // missing planes
+		"//planes/radius",                    // Empty segment
+		"/",                                  // Empty segment
 	}
 	for _, datum := range data {
 		planeType, planeName, remainder, err := ExtractPlanesPrefixFromURLPath(datum)

test/ucp/httpbaseline/baseline.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"html"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -202,7 +203,11 @@ func (rt *RoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
 	}
 
 	w.WriteHeader(w.Code)
-	_, err = w.WriteString(rt.Request.Body)
+
+	// We need to escape/sanitize the content to prevent XSS attacks.
+	// Please see: https://github.com/radius-project/radius/security/code-scanning/2
+	safeContent := html.EscapeString(rt.Request.Body)
+	_, err = w.WriteString(safeContent)
 	if err != nil {
 		return nil, err
 	}