[enhancement] Make TOKEN parameter optional inside HeadersConfig/ApiOptions

[DarkHelmet67]

Actually calling a public web service without a token appends "Authorization: Bearer" to request headers, which can cause issues. Can we make it optional like ID and VERSION?

export type HeadersConfig = {
  id?: string,
  version?: string,
  token?: string
};

[StefanoMagrassi]

The api layer is specific to Contactlab's requirements so the token is mandatory in order to interact with our APIs.

The request layer already gives you enough "power" to develop a custom solution when you need to decode/validate a response without specifing a token in the request (e.g. in order to fetch a json file).

import {ApiTask, ApiError, DecoderError} from '@contactlab/appy/lib/api';
import {AppyResponse, Mixed, get} from '@contactlab/appy/lib/request';
import * as t from 'io-ts';
import {fromEither} from 'fp-ts/lib/TaskEither';

// --- Define decoder
const fooBar = t.interface({
  foo: t.string;
})
type FooBar = t.TypeOf<typeof fooBar>;

// --- Fn in order to handle decoding
const applyDecoder = <A>(
  aresponse: AppyResponse<Mixed>,
  decoder: Decoder<Mixed, A>
): Either<ApiError, AppyResponse<A>> =>
  decoder
    .decode(aresponse.body)
    .bimap(err => new DecoderError(err), body => ({...aresponse, body}));

// --- Get the json from url with decoder, but without token
const getJson = <A>(url: string, decoder: Decoder<Mixed, A>): ApiTask<FooBar> => 
  get(url, {} /*any request configuration*/)
    .mapLeft<ApiError>(x => x)
    .chain(resp => fromEither(applyDecoder(resp, decoder)))

// --- Make the Task
getJson('https://my.json.com', fooBar);