Foreman » Smart Proxy

There is no locking used during `read`, only `write`. If the token file is being rewritten, a `read` that happens during the write can get an empty file. The code then explodes with...

```
Failed to enable autosign for host.example.com: undefined method `push' for nil:NilClass
/usr/share/foreman-proxy/modules/puppetca_token_whitelisting/puppetca_token_whitelisting_token_storage.rb:42:in `add'
/usr/share/foreman-proxy/modules/puppetca_token_whitelisting/puppetca_token_whitelisting_autosigner.rb:59:in `autosign'
```

It's also possible to lose updates. Two concurrent adds can both read the same old YAML array, append different tokens, then serialize their writes with the last writer winning.

I suspect other people haven't hit these bugs as they're almost certainly using Foreman itself as the smart-proxy client. I'm using terraform to build hosts and calling the API from a datasource in that...