This is on purpose NOT $ReadOnly - seems like fetch() doesn't like the plus sign 😛

I really don't like passing this param all the time but haven't got any better idea than possibly this:

1. Create higher-order-function (curry this one) in lib: const httpAuthorizationHeaderFactoryFn = b64encodeFn => authMetadata => { ... }
2. For each platform create {keyserver,native,web}/utils/some-utils.js with
   • keyserver: const createHTTPAuthorizationHeader = httpAuthorizationHeaderFactoryFn(the_above_Buffer_from_fn);
   • native: const createHTTPAuthorizationHeader = httpAuthorizationHeaderFactoryFn(some_fns_from_commUtilsModule);
   • web: const createHTTPAuthorizationHeader = httpAuthorizationHeaderFactoryFn(btoa);

But the above is still not perfect. Let's assume I want to add another utility function on top of this one:

function createDefaultHTTPHeaders(authMetadata: AuthMetadata): { [string]: string } {
  const authorizationValue = createHTTPAuthorizationHeader(authMetadata);
  return {
    Authorization: authorizationValue,
  };
}

I'd have to repeat this function 3 times per platform, or curry the same way as the original: const defaultHTTPHeadersFactory = authHeaderFn => authMetadata => { ... }