error: Non-JSON reply

[sdebaun]

API calls fail with unhelpful error when authed. I get the same error whether I run the app directly, or access the API call through the explorer:

Reproduction steps:

1. cloned repo
2. changed WEB_CLIENT_ID in helloworld_api.py
3. changed CLIENT_ID in base.js

I can't believe that this example doesn't work out of the box. What am I doing wrong? What is the error message trying to tell me?

[sdebaun]

Note, it works fine when I'm not authed when I make the call.