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.

docs/usage/oauth2.md

@@ -10,6 +10,7 @@ appName | `OAUTH_APP_NAME` |application name, displayed in authorization popup.
 scopeSeparator | `OAUTH_SCOPE_SEPARATOR` |scope separator for passing scopes, encoded before calling, default value is a space (encoded value `%20`). MUST be a string
 additionalQueryStringParams | `OAUTH_ADDITIONAL_PARAMS` |Additional query parameters added to `authorizationUrl` and `tokenUrl`. MUST be an object
 useBasicAuthenticationWithAccessCodeGrant | _Unavailable_ |Only activated for the `accessCode` flow.  During the `authorization_code` request to the `tokenUrl`, pass the [Client Password](https://tools.ietf.org/html/rfc6749#section-2.3.1) using the HTTP Basic Authentication scheme (`Authorization` header with `Basic base64encode(client_id + client_secret)`).  The default is `false`
+usePkceWithAuthorizationCodeGrant | `OAUTH_USE_PKCE` | Only applies to `authorizatonCode` flows. [Proof Key for Code Exchange](https://tools.ietf.org/html/rfc7636) brings enhanced security for OAuth public clients. The default is `false`
 
 ```javascript
 const ui = SwaggerUI({...})
@@ -21,6 +22,7 @@ ui.initOAuth({
     realm: "your-realms",
     appName: "your-app-name",
     scopeSeparator: " ",
-    additionalQueryStringParams: {test: "hello"}
+    additionalQueryStringParams: {test: "hello"},
+    usePkceWithAuthorizationCodeGrant: true
   })
 ```