Allow setting additional body params for token request

[big-mike-88]

When calling getTokenFromCodeRedirect, I need to be able to set additional body params. Postman lets me do this and I get something like:

Content-Type: application/x-www-form-urlencoded
Authorization: Basic blablabla=
User-Agent: PostmanRuntime/7.43.3

grant_type: "authorization_code"
code: "661ccc4061c4ba39b6166cc02411a1202cabb9b0ac46a4ee8b249e82ab0fe160"
redirect_uri: "https://test.com"
extra_param: "extra_val"