Signature needs region when using AppSync custom domains

[danielsharvey]

When using AppSync custom domains (https://docs.aws.amazon.com/appsync/latest/devguide/custom-domain-name.html), the produced signature does not contain the region (cannot be inferred from URL) and so the auth fails.

I have tested a fix by inserting region: "ap-southeast-2", after line 34:

appsync-client/src/createRequestObject.ts

Lines 30 to 42 in aeedb2b

	return {
	host,
	method: "POST",
	path,
	service: "appsync",
	headers: {
	"Content-Type": "application/json",
	},
	body: JSON.stringify({
	query: rawQuery,
	variables,
	}),
	};

Of note, the library does not report this error well. I have tested at fix by inserting the following in the the result.on("end", ... processing (line 21 below):

if (result.statusCode !== 200) {
  // reject(new Error(`Error: Status Code ${result.statusCode}`));
  console.log('STATUS CODE', result.statusCode);
  console.log('STATUS RESPONSE', rawResponseBody);
}

appsync-client/src/httpsRequestPromisified.ts

Lines 20 to 37 in aeedb2b

	result.on("end", () => {
	try {
	// JSON parse the response body
	const body = JSON.parse(rawResponseBody);
	// Reject if no data
	if (!body.data) {
	reject(Error(rawResponseBody));
	}
	// Resolve with just that data
	resolve(body.data);
	} catch (e) {
	// Throw the full body if it isn't JSON (usually this is where a GraphQL server is responding with e.g. an
	// error page instead of a properly formatted GraphQL error.)
	reject(Error(rawResponseBody));
	}
	});

I can submit a PR soon unless someone beats me to it.

[danielsharvey]

This is probably the same / related to #24.