title: "INVALID" is not a valid start token
body: <p>Can't for the life of me figure out why I'm getting this error for one of the applications I'm trying to scrape.  I have the following prometheus.yml:</p>
  
  <pre><code># prometheus.yml
  global:
      scrape_interval: 5s
      external_labels:
          monitor: 'my-monitor'
  
  scrape_configs:
      - job_name: 'prometheus'
        metrics_path: /metrics
        static_configs:
            - targets: ['localhost:9090']
      - job_name: 'app'
        metrics_path: /custom_metrics
        static_configs:
            - targets: ['host.docker.internal:8888']
        basic_auth:
            username: user
            password: pass
      - job_name: 'otherapp'
        metrics_path: /custom_metrics
        static_configs:
            - targets: ['host.docker.internal:8081']
        basic_auth:
            username: admin
            password: admin
  </code></pre>
  
  <p>I'm running prometheus with docker and both applications are running on my local host.  'app' is being scraped fine but I'm seeing the following in the targets section of the Prometheus UI:</p>
  
  <p><a href="https://i.stack.imgur.com/aF7i4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aF7i4.png" alt="prometheus ui"></a></p>
  
  <p>I've run the above configuration against <code>promtool check config</code> with no complaints and I've also run the metrics from both of my applications through <code>promtool check metrics</code> with no complaints other than warnings about missing 'help'</p>
  
  <p>I can hit the urls from the screen shot locally just fine and use the basic_auth username and pass from the config to see the metrics.</p>
  
  <p>At this point I'm at a loss as to how to proceed.  Is there something wrong with my config?  Is there something that might be wrong with my metrics that promtool wouldn't catch?</p>