Unable to obtain access token via GitHub Enterprise

[Zachary Piazza]

Hello,

I am trying to use gidgethub to build a GitHub App for some automation tasks. I was able to install and test the app on public GitHub without any problems. However, when I tried to port the application over to our company's GH Enterprise instance, I'm getting an exception thrown on the get_installation_access_token method. The response just says: gidgethub.BadRequest: Not Acceptable

If I use the get_jwt function myself and then use Postman or equivalent tool, I am able to POST a request to the access_tokens endpoint and see a token returned to me. Here is the relevant snippet:

@routes.post('/')
async def main(request):
    try:
        body = await request.read()
        event = sansio.Event.from_http(request.headers, body, secret=GH_SECRET)
        print('GH delivery ID', event.delivery_id, file=sys.stderr)

        if event.event == "ping":
            return web.Response(status=200)
        async with aiohttp.ClientSession() as session:
            gh = gh_aiohttp.GitHubAPI(session, "zachary-piazza", base_url='https://github.hpe.com/api/v3')
            access_token = await get_installation_access_token(
                gh, installation_id=GH_INSTALLATION_ID, app_id=GH_APP_ID,
                private_key=GH_PRIVATE_KEY
            )
            gh = gh_aiohttp.GitHubAPI(session, "zachary-piazza",
                                      oauth_token=access_token['token'],
                                      cache=cache, base_url='https://github.hpe.com/api/v3')
            # Give GitHub some time to reach internal consistency.
            await asyncio.sleep(1)
            await router.dispatch(event, gh)
        try:
            print('GH requests remaining:', gh.rate_limit.remaining)
        except AttributeError:
            pass
        return web.Response(status=200)
    except Exception as exc:
        traceback.print_exc(file=sys.stderr)
        return web.Response(status=500)

Am I doing something wrong in my my call to get_installation_access_token? Any help here would be appreciated. Thank you!