Fix authenticate() ctx properties being missing

This was broken because the return value of `initialize()` was a `Promise<...>` but its caller wasn't `await`-ing the value.

This was causing the `gcpIap` provider to fail on the `/request` endpoint because `jwtHeader` was undefined.

The OAuth equivalent keeps `initialize()` synchronous, and all implementations don't _need_ to be `async`, so make them synchronous instead.

I've chosen the changelog to be a `major` bump since this changes the API of a public type.

Signed-off-by: Mitchell Hentges <mhentges@spotify.com>

plugins/auth-node/api-report.md

@@ -550,7 +550,7 @@ export interface ProxyAuthenticator<TContext, TResult> {
   // (undocumented)
   defaultProfileTransform: ProfileTransform<TResult>;
   // (undocumented)
-  initialize(ctx: { config: Config }): Promise<TContext>;
+  initialize(ctx: { config: Config }): TContext;
 }
 
 // @public (undocumented)

plugins/auth-node/src/proxy/types.ts

@@ -21,7 +21,7 @@ import { ProfileTransform } from '../types';
 /** @public */
 export interface ProxyAuthenticator<TContext, TResult> {
   defaultProfileTransform: ProfileTransform<TResult>;
-  initialize(ctx: { config: Config }): Promise<TContext>;
+  initialize(ctx: { config: Config }): TContext;
   authenticate(
     options: { req: Request },
     ctx: TContext,