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.

src/core/plugins/auth/actions.js

@@ -120,13 +120,14 @@ export const authorizeApplication = ( auth ) => ( { authActions } ) => {
 }
 
 export const authorizeAccessCodeWithFormParams = ( { auth, redirectUrl } ) => ( { authActions } ) => {
-  let { schema, name, clientId, clientSecret } = auth
+  let { schema, name, clientId, clientSecret, codeVerifier } = auth
   let form = {
     grant_type: "authorization_code",
     code: auth.code,
     client_id: clientId,
     client_secret: clientSecret,
-    redirect_uri: redirectUrl
+    redirect_uri: redirectUrl,
+    code_verifier: codeVerifier
   }
 
   return authActions.authorizeRequest({body: buildFormData(form), name, url: schema.get("tokenUrl"), auth})