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.

dev-helpers/index.html

@@ -62,7 +62,8 @@
         realm: "your-realms",
         appName: "your-app-name",
         scopeSeparator: " ",
-        additionalQueryStringParams: {}
+        additionalQueryStringParams: {},
+        usePkceWithAuthorizationCodeGrant: false
       })
     }
   </script>