A RequestRewriter must be set (even if just the do-nothing ANONYMOUS rewriter) before a server can be contacted. (The Fetcher cannot make assumptions and default to an anonymous access attempt, since we do not want to spam requests to a server which requires login before the login rewriter is ready).
The
RewritingFetcheris a fairly thin layer around the nativefetchmethod, allowing asynchronous manipulation of the request before it is sent. The primary motivation is adding authorization headers, likely based on a refresh token, but the rewriter can in principle manipulate the request in any way.