feat: add PKCE support for OAuth2 Authorization Code flows (#5361)

* Add PKCE support.

* Fix tests

* Update oauth2.md

* Rename usePkce

* Fix the BrokenComponent error

* Update oauth2.md

* Remove isCode variable. Remove uuid4 dependency.

* Remove utils functions

* Import crypto

* Fix tests

* Fix the tests

* Cleanup

* Fix code_challenge generation

* Move code challenge and verifier to utils for mocks. Update tests.

* Mock the PKCE methods in the utils file properly.

* Add missing expect

* use target-method spies

* Add comments to explain test values.

* Get rid of jsrsasign.

test/mocha/core/utils.js

@@ -28,6 +28,8 @@ import {
   getSampleSchema,
   paramToIdentifier,
   paramToValue,
+  generateCodeVerifier,
+  createCodeChallenge,
 } from "core/utils"
 import win from "core/window"
 
@@ -1402,4 +1404,27 @@ describe("utils", function() {
       expect(res).toEqual("asdf")
     })
   })
+
+  describe("generateCodeVerifier", function() {
+    it("should generate a value of at least 43 characters", () => {
+      const codeVerifier = generateCodeVerifier()
+
+      // Source: https://tools.ietf.org/html/rfc7636#section-4.1
+      expect(codeVerifier.length).toBeGreaterThanOrEqualTo(43)
+    })
+  })
+
+  describe("createCodeChallenge", function() {
+    it("should hash the input using SHA256 and output the base64 url encoded value", () => {
+      // The `codeVerifier` has been randomly generated
+      const codeVerifier = "cY8OJ9MKvZ7hxQeIyRYD7KFmKA5znSFJ2rELysvy2UI"
+
+      // This value is the `codeVerifier` hashed using SHA256, which has been
+      // encoded using base64 url format.
+      // Source: https://tools.ietf.org/html/rfc7636#section-4.2
+      const expectedCodeChallenge = "LD9lx2p2PbvGkojuJy7-Elex7RnckzmqR7oIXjd4u84"
+
+      expect(createCodeChallenge(codeVerifier)).toBe(expectedCodeChallenge)
+    })
+  })
 })