Await signature verification function in backend

[mkurapov]

Context

We are currently not awaiting the verifyApiSignature function in the Admin API middleware:

rafiki/packages/backend/src/app.ts

Lines 386 to 393 in b83ac58

	if (this.config.adminApiSecret) {
	koa.use(async (ctx, next: Koa.Next): Promise<void> => {
	if (!verifyApiSignature(ctx, this.config)) {
	ctx.throw(401, 'Unauthorized')
	}
	return next()
	})
	}

Since the function always returns a Promise instead of a bool, it effectively allows us to pass signature validation no matter the result of the function itself.

Todo

• Await signature verification in backend